Which animal do you think is "the king of the animals", the elephant, the lion or the tiger? They are all large and strong. But I think the tiger is "the king of the animals". If you watch carefully, you can find some black lines on the tiger's forehead(前额). The lines look like the Chinese word "WANG". The word means "the king of the world" in Chinese.
   Most of the tigers come from China and India. Tigers are dangerous animals. They look scary(吓人的). They like eating meat. They have yellow fur with black lines. They usually weigh about 200 to 300kg. Tigers can run fast. They run at a speed of 20 meters per second.
Some people think they are dangerous. But they don't know tigers are in danger now. There are only 20 to 30 wild South China Tigers in China and less than 300 in the world. Lots of people kill them for their fur. We should take action to protect them.

Look up in the sky. Do you see any clouds? What do they look like? Some clouds are fluffy(绒毛状的) and white, like cotton balls. Others are dark almost black, and make you hold an umbrella. At sunrise and sunset, clouds can look red, purple, or yellow—as if they were colored with crayons. But what are clouds anyway?

    You can't reach out and touch the clouds, but you can make your own in a bottle.

    You need

    * an adult helper

    * a huge, empty glass jar

    * a metal strainer(过滤器)

    * hot water

    * ice

    Do these

    Step1. Have your helper fill the jar with hot water, leave it there for two minutes, then pour out most of the water. Leaving just an inch or two at the bottom of the jar.

    Step2. It's your turn, put the strainer over the mouth of the jar, fill the strainer with ice. Watch the jar.

    What happened?

    A cloud formed in the jar! Some of the hot water at the bottom of the jar turned into hot water vapor(蒸汽). The water vapor rose and met with the cold air coming off the ice. When the water vapor condensed, it formed a cloud. Hot air rises and carries with it lots of water vapor, the higher the air rises, the more it cools down. Soon the cold air can't hold all the water vapor so it starts turning into tiny water drops, and becomes a cloud.

    A city without cars would be very strange, right? But Venice is such a city.

    Venice is in the northeast of Italy. It wasn't built on land, like Beijing or Shanghai, but on more than 110 islands. Seawater is everywhere around the city.

    Even so, travel isn't difficult. The waterways have always been the best way to get around. There are 117 waterways and more than 400 bridges that can guide you where you want to go.  People in Venice move from place to place by boat.

    Water makes the city special, but it is also a big problem. Sometimes tourists will have such strange experiences. One moment they walk across the Rialto Bridge, and there's nothing special. But when they come back to the bridge an hour later, it's underwater and everyone is wearing rain shoes.

    Once, people used too much underground water. This made the city get lower little by little. Now the city has gone down by 23 centimeters. Another problem is the rising seawater. The temperature has risen over the years. This has made the ice of the Arctic Ocean (北冰洋) melt( 融化). Every year, high waters hit the city in autumn and winter. When a lot of water comes, more than half of the city is underwater.

    Scientists are trying different ways to stop the city from getting even lower. The Italian government has asked some of Italy's biggest companies to build the MOST project, which was planned to be build under the seawater to stop the rising water. Anyway, this project is helping solve the problem.

    Could smells affect your lifespan? Female fruit flies (果蝇) without the ability to smell food live longer than other fruit flies．The sense of smell may be connected to the cellular ageing (细胞老化) process in many other living things  even people．Such connection has recently been found in both worms and flies．For example, scientists found that removing fruit flies' ability to smell made them live nearly 20 percent longer than flies with a sense of smell．

    They confirmed that food smells were the ones most likely to affect ageing, as nutrition (营养) and lifespan are known to be connected in many living things．To test the idea that food smells affect lifespan, they removed flies' ability to smell carbon dioxide, which is produced by some fly foods．They left the rest of the smelling system．

    This action had no effect on male flies, but the females lived 30 percent longer than normal．Removing the ability to smell CO₂ may stop flies getting information about food availability．This could mean that food is not enough, causing processes that encourage flies to survive．Scientists found that the female flies from stored extra fat and that both males and females immune (免疫) to CO₂ were stronger against the stress than normal flies．It is suggested that females may simply be easily influenced by the smells of CO₂ ．

    Scientists point out that people don't know whether ageing and smell are connected in animals and humans．But they clearly experience physical changes after smelling food．

    No Car Day first started by 34 cities in France on September 22, 1998. People started it to protect the environment. By now, more than 1,000 cities around the world have a No Car Day.

    The first No Car Day in China was in Chengdu in 2001. Other cities, including Taipei, Shanghai and Wuhan, also support(支持) the day.

    In Beijing, more and more people are joining in the program. It asks drivers to leave their cars at home for one day each month and walk or ride a bike to work. It also calls on Beijingers not to use cars on June 5(World Environment Day). The slogan(口号) for the day is, "If we drive for one less day, we can have one more nice day."

    So far, more than 200,000 drivers Show their support. "We can't decide the weather, but we can choose not to drive," said Wu Zhonghua, a car dub manager. Beijing is trying to have 238 blue sky days this year. In the first quarter of 2017, Beijing only had 52 blue sky days. This was 11 days less than the number for the same period the year before.

    We must do more for No Car Day.

    There is one thing. We can't see it. Sometimes we can hear it and even feel it. Without(没有) it, all the living things will die. Do you know what it is? Oh, it is air.

    However, what's the air like today?

    In cities, there are too many people and too many cars on the roads. The cars send out (排放) a lot of bad gases(气体) In cities, there are many chemical factories(化工厂). They send out terrible smoke every day. This kind of smoke is very bad for our health. Now the air is becoming worse and worse. Every day, we breathe (呼吸) the bad air in and out. This is very unhealthy for us and it makes us feel sick.

    To keep us healthy, we have to go to the countryside to breathe more fresh air. Or we can go up hills to get more fresh air.