[求助]大全723

1.        The debate over bilingual education centers on the issue of whether the United States should foster the idea of single common language, an idea, some believe, that has in the past been crucial in binding diverse constituencies together.

(A) been crucial in binding diverse constituencies together

(B) been crucial as a binding together of diverse constituencies

(C) been crucial to bind together constituencies that are diverse

(D) become crucial in binding together diverse constituencies（A）

(E) become crucial to bind together constituencies that are diverse

这句子的主语是debate，谓语动词是什么？如果是believe，那前面的an idea,some又是什么？

另外，为什么选A，能说说其他每个选项的错误吗？谢谢！

crucial in/to doing something 惯用法。an idea=the idea of single common language，some=某些人

C的became和be的意思不同。