从基本工作原理方面的差别来看，航空活塞发动机主要有四行程和二行程发动机两种。
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After _______ him the capsules at eleven o' clock I went out for a while.
A. give
B. gave
C. given
D. giving
I took my dog for a walk up the road and along a _______ creek.
A. freeze
B. froze
C. frozen
D. freezing
We found a _______ of quail under a high clay bank.
A. bunch
B. school
C. covey
D. fleet
I killed two birds as they went out of _______ over the top of the bank.
A. sight
B. space
C. style
D. shape
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