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
What is NOT a change to the literature class
A．Class location.
B．Class times.
C．Class length.
D．Class size.
单项选择题
When supply exceeds demand for any product, prices are ______ to fall.
A．timely
B．liable
C．simultaneous
D．subject
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