如图所示，为一皮带传动装置，右轮半径为r，a为它边缘上一点；左侧是一轮轴，大轮半径为4r，小轮半径为2r，b点在小轮上，到小轮中心的距离为r。c点和d点分别位于小轮和大轮的边缘上。若传动过程中皮带不打滑，则

①a点和b点的线速度大小相等

②a点和b点的角速度大小相等

③a点和c点的线速度大小相等

④a点和d点的向心加速度大小相等

A. ①③

B. ②③

C. ③④

D. ②④

---Tom is so worried about the test that he said he was going to study all night.

----Tell him he should quit _________and get some help. 

A．to have worried

B．to worry

C．worring

D．from worrying