PREP07-SC2-08题 时态问题（过去完成时）

tong5211

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

Ozone, a specialform of oxygen that screens out harmful ultraviolet rays, reaches highconcentrations twelve miles above Earth, where it has long appeared that itwas immune from human influence; we have now realized, though, thatemissions of industrial chlorofluorocarbons deplete the ozone layer.

(A) has longappeared that it was immune from

(B) has longappeared to have been immune from

(C) has longappeared as being immune to

(D) had longappeared immune to

(E) had longappeared that it was immune to

正确答案是D，求问，为什么可以用过去完成时had long appeared呢？？
语法笔记里的解释是：

(A) it has long appeard that中it是形式主语，后面的it是指Ozone，两个it指代对象不一致。

(B) appeared to have been immume中的现在完成时多余，因为前面has appeared已经表达了完成时

态。

(C) appear as being用法错误。

(D) 正确，appear用作系动词，immune是adj.，简洁明了。分号后面是have now realized，强调now，

用了现在完成时，分号前面的long强调与现在的对比，用过去的时态较合理。

(E)  两个it指代不一致。

解释力业没有说A,B,C的现在时是错误的，那可不可以理解为，这一题where从句部分，可以用现在完成时也可以用过去完成时？？
我之前一直以为，在一句现在时基调的句子里，没有过去时的话，不可以使用过去完成时。。。
但这个句子就没有过去时，可以使用过去完成时。。。于是我凌乱了。。。求各位大神帮助！

lindberghya

同问，一起等大牛牛指教~

tong5211

顶上去，求大神答疑！！

soulwangh

1 Grammatically speaking :when it is a point verb(happen and finish simultaneously), present perfect can be a past time point.
2 Logically speaking: realize happens in the past(according to No 1). The author wants to emphasize that "appear" happened and finished preceding "realize" and would not happen once again. According to chronological relationship and the logical meaning, past perfect is best.