在四冲程汽油机工作时，有一个气门开启，另一个气门关闭，且活塞在向气门靠近的冲程是__________冲程。
排气
The reason _____ he could not go there was_____ his grades were too low. [ ]
A. why; because
B. why; that
C. for which; which
D. for which; 不填
血浆凝血酶原时间延长见于下列情况，但除外()
A．肝硬化
B．维生素K缺乏
C．阻塞性黄疸
D．用肝素后
E．用华法林后
