—Remember how we met for the first time, Dick?

—Of course I do．You ______ to the teachers’ office hurriedly and ______ me．

A．had walked; weren't noticing

B．were walking; didn't notice

C．had been Walking; noticed

D．walked; had noticed

两重物的质量均为m，分别系在两软绳上，此两绳又分别绕在半径各为r与2r并固结一起的两圆轮上。两圆轮构成之鼓轮的质量亦为m，对轴O的回转半径为ρ_o。两重物中一铅垂悬挂，一置于光滑平面上，当系统在左重物重力作用下运动时，鼓轮的角加速度α为：().

A.A

B.B

C.C

D.D