He with his friends _____ chatting on the Internet. [ ]
A. is
B. are
C. am
D. be
答案:A
正常人射精30~60分钟内精子活动率至少应大于()
A.40%
B.50%
C.60%
D.70%
E.80%
根据《华润置地写字楼物业服务标准》要求,标准楼层区域室内的蟑螂成虫或若虫,阳性房间不超过()。
A.5%
B.8%
C.3%
D.10%