请教一道大全!

1.       The Audubon Society and otherconservation groups, concerned over what they have perceived to be theserious threatening of the environment as posed by the policies of thegovernment, are preparing for a major political effort.

(A) have perceivedto be the serious threatening of the environment as

(B) perceived asthe serious threat to the environment as

(C) perceive beingthe serious threat to the environment

(D) are perceivingas the serious threatening of the environment（E）

(E) perceive asthe serious threat to the environment                          正确答案是E为什么不选B