A. can be released while under strain B. is used for boat falls C. is used for extra heavy loads D. is used for light loads only
A. VB2 B. VB1 C. VD D. VC
A. 多让幼儿唱歌和朗诵 B. 多多练习 C. 反复纠正 D. 不许说话
A. 硬件系统 B. 软件系统 C. 计算机系统 D. 操作系统