已知质点运动方程为S=t3-t+2（S的单位是m，t的单位是s），则该质点在t=2s时刻的瞬时速度为（ ）m/s。
11
The new model ________ the market in three months, all the shops are now selling the old model at
a discount.[ ]
A. hitting
B. hit
C. having hit
D. to hit
—Mary, are you sure your aunt ___ back from America?
—Yes. My mother ___ me. I am going to see her now.
A．has come; told
B．came; had told
C．had come; tells
D．is coming; has told
