下述关于固有口腔境界的描述，错误的是（）
A.前界为牙列
B.上界为腭
C.下界为舌下区
D.两侧为颊
E.后界为咽门
参考答案：D
He failed the mid-term examination and only then _____ how much time he had wasted. [ ]
A. he realized
B. did he realize
C. he had realized
D. had he realized
通用文种是指什么？
