Ben ___ _ breakfast every day. [ ]
A. have to
B. has to
C. has to have
D. has to has
答案:C
There were three ___ eggs in the basket.
A.dozen
B.dozens
C.dozens of
D.dozened of
计算麻疹疫苗接种后作血清检查的阳转率,分母为()
A.麻疹易感人群
B.麻疹患者数
C.麻疹疫苗接种人数
D.麻疹疫苗接种后的阳转人数
E.麻疹疫苗接种后的阴性人数