在牙龈固有层组织中,下列哪一组胶原纤维有助于游离龈附着在牙上
A.龈牙组B.牙槽龈组C.环行组D.牙骨膜组E.越隔组
参考答案:C
Only after he realized the significance of mastering two languages __________ English carefully.
A.did he set about learning
B.did he set out learning
C.had he set about learning
D.had he set out learning
减少侵犯行为的方法与途径有______、运用社会制约和______。