______ environment is getting worse and worse because we human go against ______ nature. [ ]

A. The; the

B. The; /   

C. An; the

D. /; the

月经的发生是由于（）

A.雌激素急剧减少

B.孕激素急剧减少

C.雌、孕激素均急剧减少

D.FSH、LH急剧减少

E.促性腺激素急剧减少