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Venus is close to Earth．It is the second planet from the Sun．Earth is the third planet from the Sun．Venus is similar to Earth in size and mass (质量).It is often described as Earth's“sister”.

    Scientists have been learning about Venus for a long time．First they looked at Venus through telescopes(望远镜)．But Venus is covered with thick(厚的)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 (航天探测器) 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 Earth．