单项选择题

We will not attack ______ we are attacked; if attacked, we will certainly counter-attack.

A. if
B. when
C. unless
D. even if
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单项选择题
The speed at which an animal lives is determined by ______ the rate at which it uses oxygen.
A. measuring
B. assessing
C. surveying
D. pleasing
单项选择题
It takes a great deal of power of ______a spaceship into space.
A. elevate
B. launch
C. flourish
D. take off
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