口服避孕药失败的主要原因（）
A.频繁性交
B.月经周期中突然排卵
C.未按要求服药
D.由于胃肠吸收障碍
E.产生耐药性
参考答案：C
Some students came to Xiushui No.1 Middle School this year, and left their parents, _____ to return home until he achieves his goal.
A．determining to not
B．not determined
C．not determining
D．determined not
接触凝血因子共同特点是（）。
A.内源凝血途径
B.外源凝血途径
C.共同凝血途径
D.纤溶系统
E.抗凝血系统
