单项选择题

A considerable amount of time and money has been invested in（）this system.

A. defining
B. implying
C. reducing
D. perfecting

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I couldn't sleep because the tap in the bathroom was（）

A．draining
B．dropping
C．spilling
D．dripping
单项选择题
When the engine would not start, the mechanic inspected all the parts to find what was at （）

A. wrong
B. trouble
C. fault
D. difficulty
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