问题补充:
The factory produces half a million pairs of shoes every year, 80% are sold abroad.
A. of which
B. which of
C. of them
D. of that
答案:
(答案→)A. of which
B. which of
C. of them
D. of that
解析:此题考查定语从句。由于两句话之间无连词,所以只能构成定语从句;非限制性定语从句要用which指代物。