致使肺梗死的血栓栓子一般来自()
A.静脉系统或右心的血栓
B.二尖瓣疣状血栓的脱落
C.门静脉的血栓脱落
D.左心房附壁血栓
E.动脉及左心房的血栓脱落
参考答案:A
The village in _______ I once worked has changed a lot. [ ]
A. which
B. /
C. that
论述旅游资源开发的效应。