如果a、b是一元二次方程x2﹣x﹣3=0的两个根,那么a3b﹣a2b的值为 [ ]
A.﹣6
B.6
C.﹣9
D.9
答案:C
25.—Can you tell me the timetable of the school bus?
—Well,the bus________here for the first trip at 6:30am.
A.will leave
B.left
C.is leaving
D.Leaves
工业自动控制系统最基本的控制规律有:位式控制、比例控制、积分控制三种。