试验研究中对照组与试验组发病率差值再除以对照组发病率，所得指标为
A．有效率
B．治愈率
C．生存率
D．保护率
E．效果指数
参考答案：D
The volcano erupted violently; yet the village at the foot of it should __________. [ ]
A. come through
B. go through
C. get through
D. pass through
