Scientists believed that the bony fish like trout ______ themselves forward with the movement of their tails, while the fins on their tops and bottoms mainly work as stabilizers
A. compel
B. expel
C. repel
D. propel
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Richard Nixon was the 37th U.S. president and the only commander-in-chief who ______ from his post because of the 1970s Watergate scandal.
A. resigned
B. designed
C. assigned
D. consigned
抓斗桥式起重机的代号是( )。
A. QS
B. QD
C. QC
D. QZ