Bicycles are used by people of all ages around the world. It's common in many cities to see thousands of bikes streaming down a street.

At first, only men rode bicycles. It was thought that only men could run machines, and that women wouldn't be able to control a bicycle. In the 1890s, though, with women's growing independence(独立), bicycles offered women a way to travel by themselves. Today, of course, men, women, and children ride bicycles.

Most bikes today have two wheels, but you've probably seen other kinds, too.

Some people start riding bikes that have three wheels. The third wheel makes the bike easier to balance. These bikes are called tricycles. As you've seen, the bi- in bicycle means "two". The tri- in tricycle means "three". Bikes with three wheels aren't just for young children. They matter to adults because bikes with three wheels can help move people or things. The most common kind of adult tricycle is the rickshaw(黄包车). Rickshaws are used as bike taxis in many parts of the world.

Some bikes also have only one wheel and no handlebars(把手). These bikes are called unicycles. The first part of the word, uni-, means "one". Riding a bike with only one wheel is a balancing act—that's why unicycles are used in the circus(马戏团).

There are also bikes with four wheels. Bikes with four wheels are called quadracycles. Again, the first part of the word refers to the number of wheels. In this case, quadra-means "four".

Some friends are eating in a restaurant. They are talking about if they need to buy cars. Andy is a worker in a factory(工厂). He doesn’t like taking a bus to work. He likes cars and he has a car. He thinks cars can make him get to work earlier.

Scott is a environment protector(环境保护者). He thinks too many cars are also bad for the air. He likes riding bicycles because it is cheap and keeps the air clean. He also tells his family and friends not to take more cars. Besides, he thinks if there are more cars, the road will become very crowded. So he doesn’t want to buy a car.

Sandy’s workplace is not very far from her house. But she is planning to buy a car. Because she thinks cars make her life more convenient(方便的)and easier. She can drive a car everywhere. In a car, she can have comfortable seats and much room to carry people and other things.

Jack loves travelling by train. Travelling by train is very comfortable. Most of the trains are air-conditioned, warm in winter and cool in summer. Jack usually chooses a non-smoking section, taking a seat by the window so he can enjoy the outside views. If it is a night train, the experience can be more exciting. He just sleeps the whole night and the next day he will be in a new city. By the way, he never has to worry about his meals. The train provides food 24 hours a day.

Travelling by train has another advantage（优点）: you may meet some old friends or you can listen to people talking about something of your interest. Last week when he was on a train, for example, he ran into a primary school classmate. They didn’t hope that they could bump into（偶遇）each other that way. They talked about many things: The games they played, the jokes they made on their classmates and the funny things they had done.