He was wearing his dark glasses to _____ his eyes from the strong sunlight. [ ]

A. defend

B. protect

C. prevent

D. stop

如图所示的皮带传动装置中，轮A和B同轴，A、B、C分别是三个轮边缘的质点，且R_A=R_C=2R_B，若皮带不打滑，则A、B、C三点的角速度之比ω_A:ω_B:ω_c =            ，向心加速度之比a_A : a_B : a_C =              。