单项选择题

We must ______ that the experiment is controlled as rigidly as possible.

A．secure
B．ensure
C．assure
D．issue
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单项选择题
Those were the graduate assistants ______ to do the research work in the lab.
A．to whom it was their responsibility
B．whose responsibility there was
C．whose responsibility was
D．of whom with the responsibility
单项选择题
The young man assured the boss that he would ______ all his energies to do the job well.
A．call on
B．call forth
C．call at
D．call off
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