原发性痛经的发生与患者月经期子宫内膜和月经血中哪种激素水平升高有关（）
A．雌激素
B．孕激素
C．雄激素
D．PRL
E．PG
参考答案：E
My father _________ Beijing many times. He _________ there again last week.
A．has been to; has gone
B．has gone to; went
C．has been in; has gone
D．has been to; went
我国已将多种职业致癌物所致的癌症列入职业病名单，但其中不包括( )。
A．石棉
B．铜
C．苯
D．砷
