质点做直线运动的v-t图象如图，则（　　）

A．在前4s内质点做匀变速直线运动

B．在2s～4s内质点做匀变速直线运动

C．3s末质点的速度大小为5m/s，方向与规定的正方向相反

D．第3s内与第4s内质点的速度方向相反

After retirement, learning a musical instrument may be harder than ______ when you were a kid.

A．it may

B．it was

C．it does

D．it did