胎儿脐静脉、脐动脉、动脉导管于出生后分别闭锁成为 _________ 、 _________ 、 _________ 。
参考答案：肝圆韧带腹下韧带动脉韧带
- Mum, may I watch TV now?
-No, you _____ finish your homework first.[ ]
A. mustn't
B. must
C. need
D. can't
举止得体的具体要求是什么？
