为防止多精子受精，卵子的机制是（）。
A.透明带反应
B.放射冠紧闭
C.卵子休眠
D.精子去能
参考答案：A
The teacher said that we ______ ten lessons by the end of this term. [ ]
A. should study
B. have studied
C. were going to study
D. should have studied
以下哪一项不是MTO计划方案维护的计算范围（）
A.全部计划对象
B.指定需求单据
C.指定计划员
D.以上选项都不正确
