大全693

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 political 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

请问一下，perceive这个时态对吗？为什么不用过去式呢 ？谢谢！