新托福阅读练习材料：Bird on a Wire

bigpig

　　Have you ever wondered why birds aren't (1)electrocuted(使触电致死) by the currents(电流) that flow through high-voltage power lines(高压电线)? Find out on this Moment of Science.
　　It’s not unusual to see lines of birds (2)perched(栖息) on power lines. But did you ever wonder why birds aren’t electrocuted by the enormous currents that flow through these high-voltage wires?
　　You might think it’s because the wires are (3)insulated(绝缘的), but they’re actually not insulated at all — that’s why downed(击落的) power lines are so dangerous. No, the only reason why birds on power lines usually aren’t electrocuted is because the wire is the only thing they’re touching!
　　Like all energy, electricity seeks (4)equilibrium(均衡，平衡), or balance. That means electricity will flow from high-energy areas to areas of less energy, always using the path of least resistance(阻力最小的方向). So if the bird has one foot on our original wire, and the other foot on, for example, the ground or on a different wire with less voltage, the bird would be electrocuted. Because the electricity would pass through the bird on its way from the high-voltage line to the lower-voltage line or the ground.
　　But as long as both of the bird’s feet are on the same wire (or wires of the same voltage), the bird is safe. The current doesn’t have anywhere else to go, so the electricity won’t pass through the bird–it stays on the path of least resistance, the wire.
　　This would work for humans, too–if you were to hang suspended from one of these wires, you wouldn’t be electrocuted, as long as you didn’t get too close to anything else, like a lighter or a telephone pole(电话线杆) or the ground. But don’t try this experiment at home! If you want proof, just look up at the birds on the wires!