女性胎儿卵巢开始分化发育是在妊娠（）。
A.15周～16周
B.17周～18周
C.9周～10周
D.11周～12周
E.13周～14周
参考答案：D
There was a large box behind the door and Peter couldn't _____ falling over it in the darkness.
A．help
B．resist
C．avoid
D．prevent
血液循环的动力器官是______．血液循环包括______循环和______循环．
