A father and his young daughter get on a bus and sit down. The conductor（售票员）comes to them for their money. The father says, "I want one ticket.”Then he gives the conductor some money. The conductor looks at the girl, then he asks, "How old are you?" The father starts to speak. But the conductor stops him, and the girl says, "I am six years old at home, and four years old in buses and trains. Father tells me that.’’ The father's face turns red. He has to take some money out of his bag and gives it to the conductor. The conductor gives him one and a half (半) tickets.

核电站的核心设备是 ____，设备内发生的 ____反应是可以控制的．

用如图所示的滑轮组提升重物，在拉力为200牛时，恰能使重360牛的货物匀速上升。当拉力为400牛时，能使多重的货物匀速上升，此时滑轮组的机械效率如何变化？（不计绳重和摩擦）（  ）