Sentence Correction

I don't want just answers. Please post with explanation.

In the face of widespread concern about environmental waste, compact disc manufacturers are attempting to find a replacement for the disposable plastic box in which they package their product.

(A) the disposable plastic box in which they
(B) the disposable plastic box where they
(C) a disposable plastic box in which to
(D) disposable plastic boxes inside which they
(E) the disposable plastic boxes in which to