选矿厂磨机的传动装置有几种?
参考答案:
三种:①皮带传动(小型磨机),②齿轮减速机传动(直径<2.7m,③同步电机直接拖动(直径>2.7m)。
What __________ Dean __________ last Saturday night?[ ]
A. is, doing
B. does, do
C. did, do
D. was, do