继电保护的作用是什么？
参考答案：
当供电系统出现故障和不正常的运行状态时，能够按预定的逻辑切除故障，保证供电系统的正常工作或缩小事故范围。
She showed the visitors around the museum, the construction _____ had taken more than three years.
A．for which
B．with which
C．of which
D．to which
什么叫累计亏空体积？
