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
To survive in the intense trade competition between countries, we must ______ the qualities and varieties of products we make to the world-market demand.
A．improve
B．enhance
C．guarantee
D．gear
单项选择题
This is an ideal site for a university ______ it is far from the downtown area.
A．provided that
B．now that
C．so that
D．in that
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