课的类型一般分为两大类，即（ ）。
A．讲授课和复习课
B．讲授课与练习课
C．讲授课和实验课
D．单一课和综合课
参考答案：D
Tom is a new student in this school. He ________ have many friends here. [ ]
A. doesn't
B. don't
C. isn't
D. aren't
DO前向MAC信道采用的是（）阶Walsh码。
A.16
B.32
C.64
D.128
