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
As all the people of the world share one earth, industrial countries should be responsible for helping ______ and ______ countries.
A．developed... underdeveloped
B．developing... underdeveloping
C．developing... underdeveloped
D．developed... underdeveloping
单项选择题
The sky-scrapers stand out ______ the blue sky.
A．in
B．against
C．under
D．beneath
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