瓣膜的作用是保证血液按一定方向流动, 下列血流方向正确的是 ( )
A．心房→心室→静脉
B．心房→心室→动脉
C．心室→心房→动脉
D．心室→心房→静脉
答案：C
心房与心室之间有瓣膜，这种瓣膜只能朝向心室开，从而保证血液只能从心房流向心室，同样，心室与动脉之间也有瓣膜，这种瓣膜只能朝向动脉开，从而保证血液只能从心室流向动脉，所以血液流动方向为：心室→心房→动脉。
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