直接引起心脏后负荷加重的瓣膜病为
A．主动脉瓣狭窄
B．主动脉瓣关闭不全
C．二尖瓣狭窄
D．二尖瓣关闭不全
E．三尖瓣关闭不全
参考答案：A
red is a symbol of warmth, it can sometimes make people feel uneasy or even frightened.
A．As
B．While
C．If
D．Since
二氧化硅可引起何种尘肺
A．石棉肺B．矽肺C．硅酸盐肺D．铁肺E．铝肺
