心室舒张时，防止血液逆流的是
A．主动脉瓣和肺动脉瓣
B．二尖瓣和三尖瓣
C．主动脉瓣和二尖瓣
D．肺动脉瓣和三尖瓣
E．主动脉瓣和三尖瓣
参考答案：A
My brother goes to school ____. [ ]
A. ride his bike
B. on bike
C. by his bike
D. on his bike
中国近代文学发展期文学创作的主要成就。
