XDF SECTION13 Q10

the audubon society and other conservation groups, concerned over what they have perceived to be the serious threatening of the environment as posed by the policies of the government, are preparing for a major olitical effort.

A have perceived to be the serious threatening of the environment as

B perceived as the serious threat to the environment as

C perceive being the serious threat to the environment

D are perceiving as the serious threatening of the environment

E perceive as the serious threat to the environment

答案是E.不知道 perceive的时态是如何确定的.麻烦大家指导一下!