PREP 一道混合时态的题目 求解

8.    (24773-!-item-!-188;#058&001691)

Ozone, a special form of oxygen that screens out harmful ultraviolet rays, reaches high concentrations twelve miles above Earth, where it has long appeared that it was immune from human influence; we have now realized, though, that emissions of industrial chlorofluorocarbons deplete the ozone layer. D

(A) has long appeared that it was immune from

(B) has long appeared to have been immune from

(C) has long appeared as being immune to

(D) had long appeared immune to

(E) had long appeared that it was immune to

怎么看出来是要用过去完成时态呢

B和C的问题是什么？

我觉得这样看，

分号后面说到 “ we have now realized,though,",注意这个地方的though和now,可以看出，现在我们意识到...,那么前面肯定就是过去一直认为 。。。，正好对应于had long appeared....，这个地方永一个过去时态，个人感觉过去完成时态也可以说得通。

时态我已经明白了，谢谢楼上

那immune from 和 to 什么区别呢

Here s an example from NewyorkTime

"This doesn’t mean, of course, that China is immune from nouveau riche posturing. Louis Vuitton and Prada bags are as avidly consumed there as they are everywhere else on the planet. But a new, more sophisticated generation of creative people and style makers seems to be taking control."