___________it in the flesh, I would never have known the drought in southwest China is so serious and people are suffering so much.

A．Had I not seen

B．If I did not see

C．Should I not see

D．Were I not seen

流行病学实验中样本大小估计的有关参数是

A．第Ⅰ类错误概率
B．把握度
C．实验组预期发病率
D．对照组发病率
E．以上均是