A:两轮的角速度相等
B:两轮边缘的线速度大小相等
C:两轮边缘的向心加速度大小相等
D:两轮转动的周期相等
中国现代化的起步是( )
在( )泥石的颗粒大而粗糙。
— I saw Helen in the school just now.
— It ______ be Helen. She has gone to the shopping center with her sister.