补充－140不明白，求解

1.        It may be another fifteen years before spacecraft from Earth again venture to Mars, a planet now known to be cold, dry, and probably lifeless.

(A) again venture to Mars, a planet now known to be

(D) venture again to Mars, a planet that is known now to be

为什么选A不选D呢？谢谢。

发错地方拉, 发到语法区吧

另外A用了同位语, 是GMAT偏爱的用法

而D用了从句a planet that is ... that is 完全可以省略成过去分词known. 而且 known now to be, 也是比较awkward 的讲法