【正确答案】不久的将来人类要离开地球，迈出巨人般的步伐去访问月球，领略身体失重、无向上或向下之分的感受。

【答案解析】[注释] It is not(was not，will not be)long before．．．意为“不多久就……”，例如：It wasn't long before he told us about this affair．(过了不久他就给我们讲了这件事。)注意区别：It is(was，would be)+多少时间+before．．，意为“……(之后)才……”，如，1)It was a long time before I got to sleep again．(过了很长一段时间后，我才又入睡。)2)It would be months before he was fit for work．(过几个月以后，他才会适应工作。)