B

    In 2017, when the high speed train. Furing, left Beijing for shanghai at a speed of 350 km/h, it amazed the world. It is China's newest high-speed train and also the fastest train in the world.

    There were 2, 959 high-speed trains running across China by 2016. They make up60 percent of the world's total high- speed trains. Chinese companies have also built more than 10 high-speed railways in Europe, Southeast Asia and South America. And the high speed trains has become a new name card for China.

    Besides the high-speed trains, many other innovations(创新)have also changed people's lives in China.

    For example, though bike sharing is not new itself China has made it much more convenient. And popular. When the Chinese bike sharing companies reached Singapore and Britain months ago, users there excited and couldn't wait to post photos of themselves riding the bikes on social media(媒体).

    Cashless payment has become a lifestyle choice in China it is common that people in China go shopping with no cash(现金)in pockets. Many people just pay with their bile phones by scanning a quick respond code(QR，二维码)from the seller. Even a person selling vegetables has a QR code.

    Many foreigners have experienced lives without carrying any cash in China. They say they can't do it when they are back home in Europe.

    China is now in a great time. It has made great achievements in innovation. They are true pictures of national strength. It seems that China is really leading in some ways. And Chinese people have every reason to believe in an even brighter future.

    Rik-rrork. That's the sound made by frogs singing at night. You might have thought the noises were just the musical sounds of ure. You probably didn't realize that you were listening to frogs' communicating with one another. These familiar sounds are not random(随意的) but are actually meaningful to frogs.

Being Heard but Not Seen

    Frogs are good at being heard but not seen. These animals have several characters that protect them n predators (捕食者 ). One is their size. Most frogs are small, which helps them hide easily. Many frogs have coloring that allows them to hide in their environment, making it difficult for predators to find them. In addition, most frogs are active at night. So it is difficult for most animals to see them in the dark.

Small but Loud

    Frogs call to tell other frogs where they are. Their voices can be very loud. But when frogs feel the footsteps of a larger animal, they become silent.

    Many of the world's frogs live in rain forests, where there are many different animals calling to their own species (物种 ) in their own ways. Frogs need to call loudly enough to be heard through the noise in order to find other frogs.

Singing with Purpose

      Peter Narins is a scientist who studies how frogs call to one another. He has learned that frogs use their calls to help them tell friend from enemy. They sing the same notes at the same volume (音量 ) each time they call. In addition, Narins has found that frogs of the same species always sing the same patterns (模式 ). These patterns are like a code that is different from other animals' calls and difficult for others to copy. Narins also observed that timing plays a role in frog calls. Many frogs call only at a certain time of night.

More Work to Do

    Scientists want to better understand the purpose of frog calls. Studies continue to explore the details of frogs' unique communication. Being heard but not seen is one way frogs stay safe. The idea that they have found a way to survive in a dangerous world is simply amazing.

    Rainforests (热带雨林) cover six percent of the earth's surface (表面). There are rainforests in many parts of the world. About 75 percent of animals live in rainforests. There are many beautiful birds, insects and so on. Some of them live on the ground, some live under the ground and others live in the trees, over 30 meters from the ground. It is always hot in the rainforests and the ground is always wet. It is also very dark there.

    The rainforests are very important for us. We need them! The trees and other plants in the forest help to make the air clean. They also help to control (控制) the temperature.

    Unfortunately, in many places, the rainforests are in danger. For example, many years ago there was a large rainforest in Java, but now there is nothing. The same thing happens now in many other parts of the world. It's time to take action to save the rainforests. We can never imagine a world without rainforests. If rainforests disappeared from the earth, we wouldn't find any trees, flowers or fruits. What's more, we wouldn't get clean air, and we wouldn't find any animals. The worst result would be that we wouldn't find any humans.

    Many of us enjoy watching animals in the world. But do you know they can teach us?

    Geese(雁), for example, teach a very good lesson about 1. In the fall, Canada geese fly to the warm south to 2 Canada's cold winter. They lift off in no order. Yet 3 they form a V shape, with one bird leading the group.

    This V shape allows geese to 4 energy. When the front bird moves its wings up and down, the resulting force of the air lifts the next one. This continues down the line. The bird 5 has the hardest job. When it gets6 , it moves behind, and another bird moves into the lead. By sharing the role, the group can travel great distances. Geese flying in a V shape can fly 70 per cent farther without 7 than birds flying alone. During the long flying journey, geese communicate with one another. They honk(鸣叫) to 8 the birds up front to keep up the speed. They also cheer each other up 9 working toward a common goal.

    What have we learned from the lovely geese's experience and skills?

    10 together! Whether it is our personal lives or our jobs, we need other people. We need the spirit of teamwork!

    Humans are going to the Moon for the first time since the last Apollo Mission( 飞行任务) in 1972, 45 years ago.

    SpaceX, a US space technology company, will send two people on a private trip around the moon. And they plan to make it happen in 2018, reported CBS News.

    The company didn't name the two people, how much they were paying or even their gender(性别). But they did say that the mission would use SpaceX's Falcon Heavy rocket and Dragon 2 spacecraft. Both of them are still in development(研发).

    The founder of the company Elon Musk mentioned that the trip would last about a week. "The plan is crazy." Mark Shelhamer, a former scientist from NASA said. "It's impossible to complete the mission. Getting to the moon is a lot more difficult than getting to the International Space Station." However, Musk believes that the trip will be a great success. The spacecraft will run on autopilot(自动驾驶) and the two space tourists will get hard training.

    "There is some risk there," Musk said. "But we'll do everything we can to minimize(将…减到最少) that risk."