单项选择题

Science is still largely ignorant ______ the causes of many kinds of cancer.

A．about
B．of
C．with
D．to
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单项选择题
The manager () that the new employees go through professional training before they started working.

A．persisted
B．insisted
C．resisted
D．assisted
单项选择题
The government is trying to do something to() better understanding between the two countries.

A．raise
B．promote
C．heighten
D．increase
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