"Hello, Auntie!” Yibai hated the sound perhaps more than the bell in her history class because that meant her cousin was coming. But mom hospitably asked the virtual housekeeper to open the door.

After coming in, her cousin immediately saw through Yibai and asked her deliberately, "Xiaobai, how do you feel recently? Do you enjoy your homework? " The tone was provocative.

“So happy!” She turned over a contemptuous look.

"Have you encountered any problems recently? Just talk it out to comfort me.”

"The historical question of the 21st century, okay?"

"Well, can't you figure out such a simple question? Did you sleep in class?"

It took Yibai a lot of effort to explain that she didn't sleep in class and didn't believe what the teacher said. "The teacher said that in the 21st century, trees could be seen casually. People didn't need to stay in the mobile city. What’s more, every household could raise animals. I know the environment in the 21st century was much better than it is now, but it's still ridiculous to stay outdoors without any protection. Won't people be burned to death? The teacher just described the 21st century as heaven.”

"Come on, in the 21st century, neither had the ozone layer been destroyed nor had global warming been so serious, OK? Don't think about it without basis." Yibai’s cousin explained.

"But how could it have changed so much in just one or two hundred years?" Yibai was puzzled.

"I suggest that we go to the museum today so that you can see the videos and photos of the 21st century to understand why the environment of the earth has been polluted so seriously, so as not to let others think you are a cross between human and pig." Hearing that, Yibai was even more disgusted with her cousin.

"I remember that there is no museum in our mobile city." Said Yibai, trying to calm down.

"You silly girl, mobile city K238 has moved to our neighborhood recently to avoid natural disasters. We are going to the museum there, and we can get there in an hour or two using a thermal spaceship."

"Remember to wear protective clothing when leaving the city!" Mom's voice came from the living room.

Yibai thought about poking some holes in her cousin's protective clothing so that he wouldn’t be so arrogant.

Though Yibai could have visited the museum with virtual reality glasses, she still chose the site visit, for she believed that only by seeing the real object could she be convinced. Every time Yibai left the city, her mom would put a large bag of compressed oxygen in her bag, as if there were no air purification systems in other mobile towns. She would also check Yibai’s protective clothing repeatedly, nagging Yibai to have an augmented reality call with her every hour. It often took several minutes, and finally, Yibai would manage to leave the extra compressed oxygen at home. Getting rid of the compressed oxygen of her mother, Yibai went downstairs in a sound-control elevator and called a driverless taxi to the port.

Taking a thermal spaceship, she left the port and arrived in mobile city K238. She took her cousin and swept into the museum, hoping to prove as soon as possible that the beauty of the 21st century that the teacher said was just created by those adults to fool the kids. After all, animals were so precious, and how could every family raise them? And the world outside the mobile city was exactly as hot as an oven in the daytime and as cold as a red lotus hell (It is said that this is an extremely cold hell, in which people will get injured seriously by the severe cold, and their blood dripping on the ground is like red lotus flowers.) at night.

"How could there be trees? Can the air mixed with all kinds of poisonous gases be used to breathe? How old am I?” But when she saw the old photos in the exhibition hall, she had to believe those were true.

"Well," she was stunned, staring at a photo. "it must have been photoshopped." It was a very strange photo for her, part of which was burnt. There was an endless grassland in this photo, like a piece of Matcha cake eaten on a birthday. Without wearing protective clothing, a child exposed his skin to the sun with his V-shaped hand. The sun was also unusually mild, and soft sunshine was gently stroking the earth, like a mother in the care of her children. These were extremely odd. The ground should have been scorched. In the case of not wearing protective clothing or not entering the thermal spaceship, people should have either been burned into charcoal blocks or frozen into ice sculptures. And grassland was even more unlikely to be there. This was a world that Yibai had never imagined.

"Of course not." Yibai’s cousin seemed to be very satisfied with her expression. She saw another group of photos. There was an old house with trees beside it. It was snowing, and the snow was spreading on the ground like cream. What surprised Yibai was that people were enjoying themselves outdoors.

"Won't they be frozen into popsicles? Since it is snowing, it must be hundreds of degrees below zero. "

"This is the winter of the 21st century. It's about 20 degrees below zero at most. So they won’t become a popsicle."

"What is winter?"

"It's a season, my silly girl! In the past, the weather was regular. There were four seasons in total. Spring is the time when everything recovers; summer is the time when it is hottest; autumn is the time when fruits are ripe, and winter is the time when it snows. Afterward, the weather was out of order and had become a natural disaster.

It turned out that what the teacher said was true. "But why did the world turn into this?"

"Let's go to the next exhibition hall."

In the other hall, Yibai found the cause of the earth's anger. The teacher once said that dolphins are extremely intelligent and kind animals. When they see someone falling into the water, they will rescue him and return him to the shore. Even if the dolphins are so cute, they are extinct. In the photo in front of Yibai, a large group of dolphins fell into a pool of blood, which was just because someone killed them without restraint to satisfy their appetites. In those photos, people's crimes were thoroughly exposed. To produce more, the black-hearted factories blackened the original pure sky regardless of the amount of exhaust gas emissions. As a result, the glaciers melted, and the ozone hole came into being; for money, poachers killed one animal after another, resulting in the imbalance of the biological chain and the extinction of species; to make new farmland, greedy farmers cut down trees endlessly, so trees could no longer produce air, and a large area of the forest turned into loess. It all came down to human desire.

"It's no less than mass extinction." Yibai was angry, frightened, and could not stop trembling.

"It's a mass extinction," Yibai’s cousin muttered. "It's exactly a mass extinction."

Before leaving the museum, Yibai bought a set of postcards showing the scenery of the earth in the early years. "Passenger, the spaceship will take off soon. Please keep your personal belongings inflammable." On the way home, Yibai reluctantly put the postcards back in her bag and continued to aftertaste the beautiful look of heaven.