单选题
Most insulation devices of this kind, ______ manufactured for such purposes, are extremely expensive to install.
A、
that are
B、
which is
C、
those are
D、
as are
【正确答案】
D
【答案解析】
[解析] 本题考查的是as的用法。这里as指代Most insulation devices of this kind。因此D项正确。
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