阅读下列短文,从每题所给的A、B、C、D四个选项中选出最佳选项。
A
Astronomy is the oldest science known to man.Thousands of years ago,man looked at the stars and wondered about the heavens.But man was limited by what they could see with their eyes alone.
The Greeks studied astronomy over 2,000 years ago.They could see the size,colour,and brightness of stars.They could see their places in the sky.They watched the stars move as the seasons changed.But the Greeks had no tools to help them study the starry heavens.
Each new tool added to the files of astronomy helped man reach out into space.Until there were telescopes(望远镜),man knew little about the moon.They did not know that the planet called Saturn(土星) had rings around it.Their sight was so limited that they could not see all the planets.In the early 1700s,people thought there were only six planets.
Before the spectroscope(分光镜),man did not know what kind of gases was in the sun or other stars.Without the radio telescope(射电望远镜),we did not know that radio noises came from far out in space.
Today,astronomy is a growing science.We have learned more in the last fifty years than in the whole history of astronomy.
21.Thousands of years ago, .
A.man watched the stars with their eyes
B.telescopes helped man to study the stars
C.man knew nothing about the sky
D.man knew Saturn had rings around it
22.When the Greeks watched the stars,they knew all of the following EXCEPT .
A.the colour of the stars
B.the size of the stars
C.the movement of the stars
D.what the stars were made of
23.Man now knows .
A.the moon has rings around it
B.there are six planets
C.Saturn’s rings can be seen by human eyes
D.radio noises come from far out in space
