影响子宫内膜由增生期转变为分泌期的激素是

A．雌激素
B．孕激素
C．促卵泡素
D．黄体生成素
E．促性腺释放激素

__________ there are a large number of chemical factories，the air is likely to be polluted.

A．That

B．Where

C．Once

D．As