Crude oil is refined in a refinery, ______makes it possible to get many grades of oils for different uses.
A、
as
B、
that
C、
this
D、
which
【正确答案】
D
【答案解析】
解析：本题考查非限制性定语从句的用法。非限制性定语从句中，从句缺少主语，指物时应用which来引导。
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