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【单选题】
第二心音产生的主要原因是A.
心室舒张期,主动脉瓣和肺动脉瓣关闭
B.
心室射血引起大血管扩张及产生的涡流发出的振动
C.
心肌收缩,房室瓣关闭和房-室血流突然中断所引起
D.
心室舒张期,室内压迅速下降引起的振动
E.
心室舒张期,动脉管壁弹性回缩引起的振动
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【单选题】With halting steps I paced the streets, and passed the ______ of The Crossed Harpoons—but it looked too expensive and jolly to dine at.
A.
character
B.
sign
C.
mark
D.
hoard
【单选题】With halting steps I paced the streets, and passed the ______ of The Crossed Harpoons--but it looked too expensive and jolly to dine at.
A.
character
B.
sign
C.
mark
D.
board
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