Men have always wanted to fly like birds. Birds can fly easily because they are light, but men's bodies are heavier.

    Men first went up into the air in balloons. These were big bags, and they were filled with gas. Hydrogen (氢气) is a useful gas for balloons. It is lighter than air. Helium is also lighter than air, but it costs a lot of money. So balloons are usually filled with hydrogen.

Balloons have to fly with the wind as they have no engines (发动机) to drive them. Later, men made airships. They are balloons with engines. They are also filled with hydrogen.

    Aircrafts (飞机) with wings now take people across the world. Powerful engines drive these machines across the sky. Some of the engines are like the engines of cars, but they are more powerful.

    There is another kind of engine, we call it the jet (喷射) engine. An English engineer invented the jet engine. At the same time, Germans were also building a jet engine. In May 1941, the English engineer's new engine was fixed in an aircraft, and the aircraft flew quite well.

    Jet engines are very powerful. Usually two to four are enough for an airplane, but some big aircraft need six. Anyone in a moving jet plane can feel the power of the engines. Jet planes can travel faster than sound. As a flying jet plane leaves its noise behind, we do not hear it until it has gone.

    Australia as a nation is less than 250 years old if the year 1770 when James Cook discovered the land is regarded as a starting point for its modern history. The short history has not produced a big wealth of cultural heritages. For this reason, Australia spare no efforts to protect its culture. The cottage of James Cook is a perfect example of the government and people's effort.

    Built in 1755, Cooks' Cottage is the oldest building in Australia, with a fascinating past. It's a must when exploring Melbourne. Originally located in Yorkshire, England, the cottage was brought to the Fitzroy Gardens by Sir Russell Grimwade in 1934. In 1901 Australia came into being with its capital in Melbourne. To celebrate the birth of the nation, a statue of Captain Cook was built in Sydney where Cook had sailed in and set his steps onto the land. Stamps were printed in honor of the English explorer. However, Australian people would have to travel all the way to Britain to admire the life of the discoverer, so Sir Russell Grimwade, an Australian businessman, offered to buy the old house of James Cook in Yorkshire and relocate it to Melbourne when Melbourne celebrated its 100th anniversary in 1934. Amazingly, each piece was carefully numbered, packed into boxes and then shipped to Australia, along with cuttings of the original coverings. It took nearly a month to reach Melbourne.

    In fact, explorer Captain James Cook never lived in the cottage-he'd been away from home for almost ten years when his father built it-but this connection to the Cook family was enough to prompt Grimwade to transport the cottage to the other side of the world.

    Today there are policemen everywhere, but in 1700, London had no policemen at all. A few old men used to protect the city streets at night and they were not paid.

    About 300 years ago, London was starting to get bigger and more and more people began to live there. The city was very dirty and many people were poor. There were so many thieves who stole money in the streets that people stayed in their houses as much as possible.

    In 1749, Henry Fielding started to pay a group of people for stopping thieves. They were like policemen and were called "Bow Street Runners" because they worked near Bow Street.

    Fifty years later, there were about 120"Bow Street Runners", but London had become very big and needed more policemen. So in 1829, the first Metropolitan (or London) Police Service was started with about 3, 000 officers. Most of the men worked on foot, but a few rode horses.

Today, London police are quite well—paid and for the few police officers who still ride horses, the pay is even higher than for the others.

Dave is my friend. His family is rich. His parents always give him lots of pocket money(零用钱). But Dave thinks his parents work very hard and it's not easy for them to make money, so he always tries to save money. He has some good ways to do it.

Dave likes books. He tells me he often buys books online, because they're cheaper. And when he is free, he often goes to bookshops to do some reading. Dave has a bike. He usually goes to school by bike instead of(代替) taking a bus. Sometimes when it rains or snows, he walks. These two ways help Dave keep healthy and save money.

Dave brings a bottle of water to school every day. When others drink juice, he enjoys water. He says water is the cheapest and the best drink.

Some students think Dave is mean(吝啬的). But I don't think so. I think he is right.

    My neighbor is a doctor. He and his wife are some of the1people I have ever met. A few years ago, we started this kind of "favor war" where one of us would do something kind for the other, such as2the driveway or building a shed, and next time the other would3to top it with another favor.

    Yesterday morning, it snowed heavily and I remembered he shoveled (铲) my driveway for me. So I took out my shovel and took care of both our driveways and sidewalks because it was my turn to do a favor4. It took a while but I finished it and got into my car for work.

That night I got a5on my door, it was my neighbor. He immediately shook my hands and thanked me for shoveling his driveway and sidewalk, so that he was able to get to work earlier and6a boy.

    "As soon as I started the car early this morning, a call came through that a young boy in our neighborhood was seriously ill.7, my partner and I were only about 2 minutes away, but the closest ambulance 10 minutes," added he. "A young boy got to live his life because you did me the favor."

    It wasn't too much8to shovel a driveway, but what I did got a young boy to see his family again, go back to school again and live his life again.9favor is too small. Even the smallest favor can make the biggest10. One favor will always be followed by another.