质量为m的物体放在粗糙的水平地面上，物体与地面之间的动摩擦因数为μ，现在物体在一水平拉力的作用下从静止开始运动，其运动的v-t图象如图所示．下列关于小物体运动过程分析正确的是（　　）

A．0-t₁内拉力逐惭减小

B．0-t₁内拉力对物体做正功

C．在t₁-t₂时间内拉力的功率为零

D．0-t₂时间内合外力做功

I____be a bit shy, but they have helped me to be          confident. Now I know that I have the ability____good work.          [ ]

A. used to, more, to do

B. be used to, more, do

C. used to, better, doing