Here are three __________.[ ]
A. bus
B. buss
C. buses
答案:C
按所列数的规律填上后面的两个数:1,-2,3,-4,5,-6,______,______.
为防止和减少薄壁工件加工时产生变形,加工时应分粗、精车,且粗车时夹松些,精车时夹紧些。( )