One of the  was invented by accident.

Kevin became a volunteer to save endangered animals

 he had no such experience.

    Time is very important to us. When and by whom were the watches or clocks 1 Perhaps nobody knows. How could we tell time if there were no watches or clocks anywhere in the world?

    The2 was probably the world's first "clock", except in the far north, where the Eskimos live. There, it's dark most of the winter, and 3 most of the summer. But 4 most of the world, people have used the sun for day. 5 you don't have a clock that shows time, you still know that when the sun shines, it's day, and that when it's dark, it's night. The sun can not only tell you whether it's day or night but also tell you whether it's morning, noon, or afternoon. When the sun is almost directly overhead, it's6.

    People who live near the sea know time from the tides (潮汐). In the daytime, for about six hours, the water rises 7on the beach. The same thing 8again at night. There are two high tides and two tides every 9 hours.

    In some places in the world the wind comes up at about the same time every day or changes direction or stops 10. In these places the wind can be the clock.

The balloon the water and .

  the theatre will be completed in September this year.

 in the fridge after the party.

The young man is twenty years old.

Great changes  in the past ten years.