二尖瓣狭窄时，体循环栓塞最常发生于
A．脾动脉
B．脑动脉
C．肾动脉
D．下肢动脉
E．肠系膜动脉
参考答案：B
螺纹联接在承受轴向载荷时，其损坏形式大多发生在截面小的部位。
— Did you call on any of your old friends when you returned to your hometown ?
—______ of them . They were all very busy .
A．Nobody
B．None
C．Both
D．Neither
