一坡三档是指在倾斜提升巷道中，必须设置一个阻车器和（）挡车栏。
A.一个
B.两道
C.三道
D.四道
参考答案：A
There __________ a teacher and some students in the classroom. [ ]
A. is
B. are
C. have
D. has
会计科目是对会计对象的基本分类。( )
