痛经的特点是( )
A.腹痛牵引腰骶B.疼痛伴肌紧张或反跳痛C.伴随行经而周期性出现的小腹疼痛D.腹痛而有晕厥E.经行时小腹略感疼痛
参考答案:C
It's too hot in the classroom. Would you mind _____ the windows, please? [ ]
A. open
B. opening
C. opened
D. to open
原料检验站负责的进厂原料实行三级编码制度,即()、()及()。