William and his party walked on the green plain. Then the sky began to clear, and the two mother stars peeped out from behind the clouds. Ranran's beautiful long hair fluttered in the breeze, setting off a sweet smile on her face. William looked confidently at the map on the computer, which showed the next checkpoint. Sure enough, when they had gone about two kilometers further, the computer said,

Checkpoint 16 is cleared. Energy charge: 1%.

Fortunately 300 meters ahead was Checkpoint 17. They got a total of 2.5% of their energy effortlessly.

At the time of the party's vigorous advance, Rebecca was covered by a piece of paper floating in front of her. "Oh!" She cried. "A clue!" Said William excitedly, "Let's see what it says."

He opened the folded note and saw the neatness of the writing. The note said,

Dear Alien Friend,

Hello! I'm Bush, owner of Leo Bookstore. I am so excited to hear that you have come! I haven't had an alien here in years.

You must have just visited Hans the engineer, right? He told me about you, and that is why I have hastily written this note to you.

I would like to ask you to do me a favor: in response to the planetary call for environmental protection, I would like to publish a more environmentally friendly kind of books. I wonder if you have any feasible way. If you do, please come to my bookstore and feel free to advise. I would be very grateful!

Bush

"Oh, I see." Said Rebecca, "Have you guys come up with anything good?"

"I don't know." Said William, having no clue, "We are not yet aware of how green his previous books are. I think we'd better find out first."

So they managed to reach the bookstore in ten minutes. "Hello, alien friends!" Bush greeted them into the store and seated them on spacious sofas.

William said, "We've just seen your note, Mr Bush. We know exactly how anxious you are, and I'm sure we can help you. It's just that we don't yet know how green your previous books are."

Bush showed them a copy of a book that had been sold four years earlier and answered, "The technology used in this version is already green, but the standards are stricter. However, the good news is that the government said this would be the last version of the environmental standards and that it would not issue a stricter version. In addition, I want to continue to make the planet more livable."

William was amazed at how environmentally conscious the inhabitants of this planet were. People on Earth had not yet become so environmentally conscious like this, even though the environment of Earth had become very habitable.

"Then please give me a rough idea of the techniques used in this book." Ranran said, "This will help us better understand its environmentally friendliness level and provide some reference for us to come up with new ideas."

"OK." Bush said, "Every book on the planet has been made from composites that consist of cellulose and hemicellulose for a long time. Not only is it cheap and readily available, but it's water-resistant as well."

"Wow, that's nice." William exclaimed, "How do you get all these ingredients?"

"We've moved away from logging and into tissue culture. We mainly cultivate reeds, bamboo and so on. This makes it possible to get large quantities of cellulose and hemicellulose quickly. In addition, this kind of technology has only one disadvantage at present, that is, the conditions are stricter. On top of that, it beats traditional logging in terms of environmental protection.

"The process is not complicated, but the final emissions are higher. Although most of them can be recycled, there is still a small proportion of materials that cannot be easily used. This needs to be improved.

"When printing, we use ester-based inks to reduce pollution. But at present, a prominent disadvantage is that the raw materials of this kind of ink can only be obtained through plant tissue culture. We haven't figured out how to make it less demanding, and this also needs to be improved.

"As for packaging and binding, all the materials we currently use comply with the latest environmental standards, so there is no need to look for new materials. It seems that you need to give particular consideration to upgrading processing and printing techniques. It would be great if you could also address the current disadvantage of plant tissue culture. My scientific level is not high enough to develop new technology by myself. But whether or not you can help me in the end, I would like to express my sincere gratitude." With that, Bush bowed to William and his party.

"We can solve these problems." William answered with assurance. Then he saw a dialog box pop up:

The document "Producing oil using CO2.docx" has been downloaded. Please click the directory below to view it.

"It's really perfect." He thought happily, "They'll have easy access to a lot of ester-based oils to make eco-friendly inks."

And he wondered, "What about the hard-to-use emissions from the process? I'd better ask what categories those emissions fall into first."

Upon questioning Bush, William learned that they were organics, and he remembered that no process had been developed on Earth to treat them.

"Organics..." He thought thoughtfully. Suddenly he had an idea. "That's it! Wonderful, wonderful! What cannot be solved by chemical methods can be solved by biological ones!"

Using the computer, he found a variety of microbes on the planet that could consume organic matter and convert it into environmentally friendly carbon dioxide and other materials. After studying it in detail, he found that it was not difficult to grow one of the smaller organisms. What made him even more excited was that it could also serve well as pets. So he decided to file the information and show it to Bush later. Meanwhile, he also searched for the materials for degrading the paper, and learned that an enzyme preparation could successfully degrade paper with ink printed.

"God help me! Mr Bush, I have a solution! Come and see!" Cried William excitedly.

"Really? Let me see." Bush sprinted to William's side.

So William showed him what had just been filed. "You see, I have a new technology that allows you to use carbon dioxide in the air to synthesize hydrocarbons, thus making more organic products. In this way, you can produce the ester oil first and then process it further. And you end up with eco-friendly ink."

"Great, I'll take it!" Bush said excitedly.

"You're welcome. Plus, I have the perfect solution for hard-to-deal emissions: you can do it with microbes!"

"What? Microbes?" There was a glint in Bush's eyes. William's words raised his interest.

"That's right. I just learned that on this planet there is a kind of microbe that consumes organic matter and converts it into something environmentally friendly, and it's not that complicated to grow. I'm sure your bookstore could sell books and nurture them at the same time if you had enough energy. It will help you solve the pollution problem perfectly. It's a great pet too! Maybe someone would like to keep it as a pet!

"I've found something extra -- one thing can help you recycle your books better!" At this point, William paused because he knew that was how he would get Bush interested.

Sure enough, Bush urged him to talk about it. So he introduced him to the new enzyme preparation and suggested that he sell it together with books. That way, users could drip enzymes onto any page when they didn't need a book. Soon the paper could be degraded.

William asked if it was possible to build a large aseptic room for plant tissue culture. Bush's answer was yes. William suggested that he invest more robots in management, both to reduce his own burden and to ensure the lowest possible failure rate. Bush said yes.

"Well, we're done!" William exulted, "You can use these technologies. I'm sure all these meet the latest environmental standards!"

"Thanks, alien friend!" Bush shook his hand excitedly and said, "You're the next camel scientist!"

"Camel scientist?" Ranran wondered, "Do you know him too?"

"You bet. He helped me adopt these current technologies. The bookstore was just open at that time. He saw my notice and he came up to me and showed me the ropes, so I had these techniques. I guess if he saw this note I posted, he would come in person. It's just that you got there first, hee-hee."

"Wow, this camel scientist is really famous!" Said Rebecca.

"We must go visit him if we have the chance!" Photon said to Natalie.

"No problem." Bush replied, "I can't express my gratitude to you for helping me so much today! If you have any problem in the future, please contact me. I will do everything I can to help you!

"Let me show you where to go. You turn left from here and follow the tarmac road to the end. It's about five kilometers. Then you'll see a recycling center. If you need a stop at the recycling center, go find this robot, Carly, and she'll lead you. 2.7km to the south side of the recycling center is a mysterious place. Very few people have been there, so I advise you to be safe. You can easily find the camel scientist's quarters after you pass there."

"Well, thank you very much! I'm sure your bookstore will become more and more famous and do more and more for the environment!" Photon said to Bush as William and his party walked out the door.

"Don't forget to buy my books!" Bush joked. The party left Leo Bookstore laughing.

"Where are we going next?" Ranran asked William.

"The computer shows that we do need to make a stop at the recycling center and then go to that mysterious place that Bush talked about. But according to the map, it's not dangerous. So I don't think we need to be on high alert, but basic security measures should be in place -- at least not without laser guns."

The others nodded and followed William toward the recycling center.