I don't know the answer _____ the question. [ ]
A. to
B. of
C. for
D. with
答案：A
最能提示二尖瓣狭窄的是
A．Graham-Steell杂音B．开瓣音C．心尖部舒张期隆隆样杂音D．第一心音亢进E．二尖瓣面容
正态曲线下面积有一定的规律，μ±2σ的面积占总面积的（）
A.80.5%
B.85.5%
C.88.5%
D.90.5%
E.95.5%
