单项选择题

______ scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else.

A. Until
B. Since
C. Once
D. Even if
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单项选择题
Operation research is a scientific method of providing executive department with a quantitative basis for decisions ______ the operations under their control.
A. regarding
B. as to
C. on
D. considering
单项选择题
Electronic computers, ______ the complicated mathematical operations, such as weather forecast and the control of satellites, can be done quickly and accurately.
A. being used
B. used
C. having been used
D. to be used
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