曳引机通常可以分为哪几种？
参考答案：
曳引机可以分为无齿轮曳引机和有齿轮曳引机两种。
设M，N，P是三个集合，则M∩P=N∩P是“M=N”的（ ）
A．充分非必要条件
B．必要非充分条件
C．充要条件
D．既非充分又非必要条件
Tom has planned a big party on Sunday and many friends _______ to take part in. [ ]
A. will invite
B. has invited
C. will be invited
D. has been invited
