卵巢分泌的天然雌激素主要是：
A．雌二醇
B．雌三醇
C．炔雌醇
D．己烯雌酚
E．雌酮
参考答案：A
It was such a ________to hear that her son was found safe and sound in the forest.
A．ease
B．assistance
C．comfort
D．relief
细胞外液中主要的阳离子是（）。
A.K+
B.Na+
C.Ca2+
D.Mg2+
E.Fe2+
