《继电保护和安全自动装置技术规程》规定，66kV单侧电源线路可装设一段或两段式电流速断保护和（）保护，必要时可增设复合电压闭锁元件。
参考答案：过电流
—The problem isn't difficult for the children to work out, is it？
—_____ . Perhaps they should have been given a more difficult one.
A．Yes, it is
B．Yes, it isn't
C．No, it is
D．No, it isn't
电动机通过一绳子吊起质量为8kg的物体，绳的拉力不能超过120N．电动机的功率不能超过1200W，要将此物体由静止起吊用最快方式吊高90m（已知此物体在被吊高接近90m时已开始以最大速度匀速上升），所需时间为多少？
