The population of the Earth is growing faster. It is important that we look after the Earth. We need it!
The Earth gives us a lot of things. We also give the Earth a lot, but some of the things are not good.

In nature, when something dies, other animals and plants get food from it. Every animal or plant gives food for other animals or plants. However, animals can’t get food from many of the things that we ‘give’ the Earth. Animals and plants can’t eat metal, plastic and glass. These things will stay in the ground for many, many years.
Some rubbish is very dangerous for plants and animals. In some places, many animals live together. One animal makes food for many more animals. If we put rubbish and chemicals in the water, the plankton(浮游生物) can die. If there isn’t any plankton, many animals have nothing to eat.
So what can we do? Don’t leave any rubbish in the countryside! Don’t make so much rubbish!
【小题1】The Earth gives us ___________.

Australia is the largest island in the world. It is a little smaller than China. 1t is in the south of the earth. Australia is big, but its population is small. The population of Australia is nearly as large as that of Shanghai.
Enough laws (法律)have been made to fight against pollution. The cities in Australia have got little air or water pollution. The sky is blue and the water is clean. You can clearly see fish swimming in the rivers. Plants grow very well.
Last month we visited Perth， the biggest city in Western Australia, and went to a wild flower exhibition (展览). There we saw a large number of wild flowers we had never seen before. We had a wonderful time. Perth is famous for its beautiful wild flowers. In spring every year Perth has the wild flower exhibition. After visiting Perth we spent a day in the countryside. We sat down and had a rest near a path(小路) at the foot of a hill. It was quiet and we enjoyed ourselves. Suddenly we heard bells ringing at the top of the hill. What we saw made us pick up all our things and run back to the car as quickly as we could. There were about three hundred sheep coming towards us down the path.
Australia is well-known for its sheep and kangaroos. After a short drive from any town, you will find yourself in the middle of white sheep. Sheep, sheep, everywhere are sheep.
【小题1】Australia is ________.

---Do you know ____________ the population of China is?
---Yes, it has the __________ population in the world, about 1.3 billion.

American cities are similar to other cities around the world: In every country, cities reflect（反映）the values of the culture. American cities are changing, just as American society is changing.
After World War Ⅱ, the population of most large American cities became smaller; however, the population shifts（转移）to and from the city reflect the changing values of American society. In the late 1940s and early 1950s, city residents（居民）became richer. They had more children so they needed more space. They moved out of their flats in the city to buy their own homes. They bought houses in the suburbs（郊区）.
Now things are changing. The children of the people who left the cities in the 1950s are now adults. Many, unlike their parents, want to live in the cities. They continue to move to Sun Belt cities and older ones of the Northeast and Midwest. Many young people are moving back into the city. They prefer the city to the suburbs because their jobs are there; or they just enjoy the excitement and what the city offers.
This population shift is bringing problems as well as some advantages. Countless poor people must leave their flats in the city because the owners want to sell the buildings or make flats for sale instead of for rent（租金）. In the 1950s, many poor people did not have enough money to move to the suburbs; now many of these same people do not have enough money to stay in the cities.
Only a few years ago, people thought that the older American cities were dying. Some city residents now see a bright, new future. Others see only problems. One thing is sure: many dying cities are alive again.
【小题1】The main idea of the passage is _________.