单项选择题

They took ______ measures to prevent poisonous gases from escaping.

A．fruitful
B．beneficial
C．valuable
D．effective
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单项选择题
That was so serious a matter that I had no choice but ______ the police.
A．called in
B．calling in
C．call in
D．to call m
单项选择题
She was so ______ in her job that she didn' t hear anybody knocking at the door.
A．attracted
B．absorbed
C．drawn
D．concentrated
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