We have always been interested in the moon. 2, 000 years ago, people already knew it moves around the earth and where it would be in the sky at different times of the year. At that time, everything about the moon was learned by watching it carefully in the sky.
When scientists could use telescopes to study the moon more closely, their ideas began to change. They could see the moon was made of rocks. Most scientists thought moon rocks would be different from those on the earth. This was because they believed the moon had once been a planet that had been caught in the earth’s gravity millions of years earlier.
In 1969, moon rocks were finally brought to the earth and studied. Much to their surprise, scientists found that, except for water, the moon and the earth were made of the same things. Once again new ideas were needed for this new information.
After years of study, most scientists now think that the moon was once part of the earth. They believe very early in its history, maybe 4 billion years ago, something about the size of Mars hit the earth. This sent billions of rocks into space around our planet. These rocks slowly joined together and after many years became the moon.
In the future, even though our ideas about the moon may change again, we will still be interested in it.
Before 1969 most scientists thought the moon was _____.

A．part of the earth billions of years earlier

B．older than the earth

C．a planet caught by the earth’s gravity

D．made of the same things as the earth

After years of study, most scientists now think _____.

A．the earth was once part of the moon

B．the moon was once part of the earth

C．something about the size of Mars will hit earth in the near future

D．a lot of rocks will slowly join together to become the other moon

From this passage we can learn that _____.

A．scientists in the past were not clever

B．scientists are so clever that they know everything

C．new information brings new ideas

D．we now know everything about the moon

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