I    my homework this afternoon.

—No, it's too cold. We'd better stay i.

—Wow! He is really a b boy.

—It          be John's. It's           small for him.

    Tornadoes(龙卷风) are whirlwinds(旋风) with speeds of up to 400 km per hour. In Britain, there were very few tornadoes in the past. Now, there are more than 50 tornadoes a year. Tornadoes are only one sign of the world's climate changes. There are many others. The number of thunderstorms is increasing, and there are more floods in some parts of the world, and there's much less rain in others. Scientists still do not know enough about the reasons for these climate changes. Most scientists think human activities are the problem.

    Cutting down trees, burning too much oil, and the increase in the number of cars are some of the things that cause the problems. Global(全球的) temperatures are rising because of these things. Scientists believe that if the temperatures continue to rise, the ice at the poles will melt(融化) .

    If the ice melts, sea levels will rise. Some islands might disappear completely. All this means that unless we do something to stop global warming now, there may be many other dramatic changes in the future.