prep2-8

torresAing

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.

(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  
答案选D，这里为啥可以用过去完成时？后面的动作we have now realized也只是现在完成时啊,过去完成时啥时候可以和现在完成时同时出现了？

sunnybyy

很好的例子，让我们一起进步

torresAing

楼上真是好人哈，又帮我解答了一个问题。
看来很多所谓的语法规则都有例外，刚看到一题也是现在完成时和过去完成时一起出现的：

17.

The success of the program to eradicate smallpox has stimulated experts to pursue what they had not previously considered possible--better control, if not eradication, of the other infections such as measles and yaws.

(A) what they had not previously considered possible--better control, if not eradication, of the other infections such as

(B) what they had not previously considered a possibility--better control, if not eradication, of such infections like

(C) something they had not previously considered possible-better control, if not eradication, of such infections as

(D) something not considered a previous possibility--better control and perhaps eradication, of other infections such as

(E) the possibility of what they had not previously considered--better control and possibly eradication of infections like
答案是C

lshlccER

这里考的是: 不能用现在完成时
it appeared的东西和we have now realized的东西是有冲突的
所以it appeared不能用现在完成时了

当然这道题也告诉我们过去分词可以和现在分词连用了：）