求助一道语法题

lovexiaok53

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
答案是 E.
为什么B 不对?
我不太清楚这个语法题的结果, 觉得主语是AUDUBON SOCIETY, 但是怎么有两个谓语啊. :Concerned over, are preparing for a major political effort.到底哪个是修饰主语的.
请好心人解释一下! THANKS A LOT !

AlienX

最後一個as多了出來, 令多句子怪怪的...
是那這的題
最好在title上state the question # and the source.