慢性胎儿窘迫的病因（）
A.微量元素缺乏
B.胎盘早剥
C.胎盘功能不全
D.遗传因素
E.胎儿畸形
参考答案：C
— What a nice day today! Let's go to the zoo.
— _____ [ ]
A. It doesn' t matter.
B. That's a good idea.
C. See you then.
D. You're welcome.
处于牙周炎进展前沿的菌斑为（）
A.窝沟处龈上菌斑
B.牙颈部的龈上菌斑
C.附着性龈下菌斑
D.非附着性龈下菌斑
E.光滑牙面处龈上菌斑
