4. This prevents us from living there.

3．Man has known a little about Mars：there is almost no oxygen on Mars and it might be about 50 degrees above zero at noon and 100 degrees below zero at night.

2．Whether we can land on Mars depends on the development of science and technology.

7．科学家们却认为人类迟早会登陆火星的。(land，certain)

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答案：[句子翻译]　1. We don’t know whether life exists on Mars.

6．登陆火星似乎只是个梦想。

5．既然火星与地球完全不同，如果我们计划有朝一日去火星的话，我们就要带上氧气、食品、衣服和住的地方。(shelter)

4．这样我们就不能在那里生活了。　 (prevent...from)

3．人类对火星有了一些了解：火星上没有氧气，火星上中午的温度可能在50度左右，而晚上则在零下100度左右了。(know a little about)

2．我们能否登陆火星完全取决于科学技术的发展。(depend on)

1．我们不知道火星上是否有生命。(whether，exist，life)