滚珠丝杠副传动特点是（）。
A、传动效率高
B、传动转矩小
C、传动平稳
D、传度精度高
E、有可逆性
参考答案：A, B, C, D, E
I didn't understand _____, so I raised my hand to ask. [ ]
A. what my teacher says
B. what does my teacher say
C. what my teacher said
D. what did my teacher said
( )一般应用于政府工程或规模较大的工程。
A．公开招标 B．邀请招标C．不定向议标 D．定向议标
