对二尖瓣狭窄病人的麻醉处理哪项不正确（）
A.注意控制心率
B.尽力避免低氧血症
C.避免酸中毒
D.避免应用氧化亚氮
E.术中可用头低足高位
参考答案：E
除数是5，商是170，余数是3，被除数是______．
Nobody knows for sure how dinosaurs died out 65,000,000 years ago. It _______ because of sudden changes of their living conditions.
A．must have happened
B．would have happened
C．should have happened
D．might have happened
