Venus（金星） is close to the earth. It is the second planet from the sun. The earth is the third planet from the sun. Venus is similar （相似的） to the earth in size and mass （質(zhì)量）. It is often described as the earth's "sister".
    Scientists have been learning about Venus for a long time. First they looked at Venus through telescopes （望遠鏡）. But Venus is covered with thick clouds. Scientists could not see Venus well through the clouds. So they made guesses about it.
    For a long time， scientists thought that Venus had water and plants. They thought Venus might have animals too. But they didn't know for sure.
    Then scientists found a way to learn more about Venus. In the 1960s， they began sending probes （航天探測器） to Venus. The probes flew through the thick clouds. They took pictures of Venus up close. They found out many things too. The probes sent the pictures and things they found out back to the scientists.
    The scientists learned a lot from the probes. First they learned that most of their guesses were not right. And they learned that Venus is very hot.
    After that， scientists knew they could not send people to Venus. But they still wanted to know more about it. So they sent new probes. These new probes took great pictures of the planet. The pictures showed that Venus has plains （平原） and mountains! And in some ways， Venus looks like the earth.

（1）. How are Venus and the earth similar？

They are similar in size and mass .

They are similar in size and mass .

（2）. Why is it hard to see Venus well through a telescope？

Because Venus is covered with thick clouds.

Because Venus is covered with thick clouds.

（3）.When did scientists begin to send probes to Venus？

In the 1960s.

In the 1960s.

（4）. Can the scientists send people to Venus？

No，they can't.

No，they can't.

（5）. What does Venus have ？

It has plains and mountains!

It has plains and mountains!