月经先后无定期的主要发病机制是
A.寒凝血瘀,冲任不畅
B.气虚统摄无权
C.水亏火旺,热扰冲任
D.痰阻经脉,血行不畅
E.气血失于调节,血海蓄溢失常
参考答案:E
We __________ in the same school since three years ago.
A.study
B.were studying
C.will study
D.have studied
反渗透水的回收率应为()左右
A、98%
B、90%
C、70%
D、75%