( )为了消除齿轮泵的困油现象,可在泵的端盖上开卸荷槽。
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I can never forget the days _______ we worked together and the days ______ we spent together.
A. which; when
B. what; that
C. on which; when
D. when; which
Smoking, _______ is a bad habit, is, however, popular.
Is oxygen the only gas _______ helps fire burn?
John got beaten in the game, _______ had been expected.
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