If you can read a clock, you can know the time of day. But no one knows what time itself is. We cannot see it. We cannot touch it. We cannot hear it. We know it only by the way we mark its passing. Fo 题目和参考答案——青夏教育精英家教网—

题目内容

If you can read a clock, you can know the time of day. But no one knows what time itself is. We cannot see it. We cannot touch it. We cannot hear it. We know it only by the way we mark its passing.

For all our success in measuring the smallest parts of time, time remains one of the great mysteries of the universe.

One way to think about time is to imagine a world without time. There could be no movement, because time and movement cannot be separated.

A world without time could exist only as long as there were no changes. For time and change are linked. We know that time has passed when something changes.

In the real world—the world with time—changes never stop. Some changes happen only once in a while, like an eclipse(月蚀) of the moon. Others happen repeatedly, like the rising and setting of the sun. Humans always have noted natural events that repeat themselves. When people began to count such events, they began to measure time.

Humans have used many devices to measure time. The sundial was one of the earliest and simplest.

A sundial measures the movement of the sun across the sky each day. It has a stick or other object that rises above a flat surface. The stick, blocking sunlight, creates a shadow. As the sun moves, so does the shadow of the stick across the flat surface. Marks on the surface show the passing of hours, and perhaps, minutes.

The sundial works only when the sun is shining. So, other ways were invented to measure the passing of time.

One device is the hourglass. It uses a thin stream of falling sand to measure time. By the eighteenth century, people had developed mechanical(机械的) clocks and watches. And today, many of our clocks and watches are electronic.

1．What makes it possible for humans to measure time?

A．The sundial was invented. B．Some natural events take place regularly.

C．The sun rises and sets every day. D．The hourglass came into being.

2．We can learn from the passage that _______________.

A．since we can’t feel it, we have no way to deal with time

B．the existence of time depends on the changes of the world

C．when the sundial was invented, people had no worry to count time

D．electronic watches make it possible to measure time without any fault

3．Which of the following statements about the sundial is wrong?

A．It doesn’t work well when it is cloudy.

B．It measures the movement of the sun across the sky each day.

C．It can only show the passing hours when the sun is shining.