A. shall B. should C. would D. had to
A. RS232 B. RS485 C. RS422 D. RS449
A. 敞开式循环冷却水和密闭式循环冷却水系统 B. 敞开式循环冷却水和直流式冷却水系统 C. 循环冷却水系统和直流式冷却水系统