Unique among bivalves, scallops swim extremely well, propelled by jets of water expelled while snapped the shell shut.
The answer is (C)
沒有疑義, sanp-->snapping
但是snap解作"突然關上"
shut也是關上
snapping 此處很明顯是動詞的分詞型態
那shut呢? 作動詞解應該不對, 但是難道"shell shut"是名詞片語?
如果是, 突然關上"shell"不奇怪, 突然關上"shell shut"可不是很怪嘛?
Thanks