单项选择题

The barrier of language keeps many scientists in prolonged ignorance of work of immediate importance to them ______at present in many countries.

A．doing
B．to be done
C．having done
D．being done
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单项选择题
When preparing elementary school test, care should be taken______.
A．not to make the vocabulary more difficult than necessary
B．not to make the vocabulary that difficult
C．so as to not make the vocabulary part too hard
D．in not making the vocabulary a problem in terms of it difficulty
单项选择题
Doctors see a connection between increase amounts of leisure time spent______ and the increased number of cases of skin cancer.
A．to sunbathe
B．to have sunbathed
C．having sunbathed
D．sunbathing
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