单项选择题

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

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单项选择题

While watching television______.

A．the telephone rang
B．we heard the telephone ring
C．we heard the telephone rang
D．the telephone was rung

单项选择题

With prices ______ so much, it is impossible for the company manager to stick to the original budget.

A．waving
B．swinging
C．fluctuating
D．vibrating

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