大全18-21

21.   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

where 无指代.  

(C) a disposable plastic box in which to

(D) disposable plastic boxes inside which they

they 指带有歧义, inside 没有in 准确.

(E) the disposable plastic boxes in which to

The key is A.

How about B and D?

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