下列计算正确的是（　　）

已知线段AB及AB上一点P，当P满足下列哪一种关系时，P为AB的黄金分割点①AP²=AB•PB；②AP=$\frac{\sqrt{5}-1}{2}$AB；③PB=$\frac{3-\sqrt{5}}{2}$AB；④$\frac{AP}{PB}=\frac{\sqrt{5}-1}{2}$；⑤$\frac{AB}{AP}=\frac{\sqrt{5}-1}{2}$．其中正确的是____ （填“序号”）

如图，电灯的灯丝电阻为2Ω，电池电动势为2V，内阻不计，线圈匝数足够多，其直流电阻为3Ω．先合上电键K，过一段时间突然断开K，则下列说法中正确的是（   ）

    “Leave a place better than you found it.” It is a 1 philosophy, but one that William Lindesay

    2 dear.On April 22, which was also Earth Day, he led twenty 3 to help clean up the Jiankou section of the Great Wall.

    “He who 4 is the owner,” William said in the 5 remarks of the cleanup event in 2000.“The Great Wall 6China, and is also one of the greatest 7 in the world.Everyone has a 8 to protect it.Every day should be Earth Day,” he said.

    During the past three decades, he has spent most of his time 9 and exploring the Great Wall and has developed his own 10 to protect the cultural relic.

    “It's a 11 thing that people are going out to enjoy themselves and to 12 the great history and heritage, 13 it's also quite dangerous if they don't 14 how fragile (易损坏的) the historical sites are and how fragile the 15 is,” William said.

    In 1989, his first 16Alone on the Great Wall was published, and he has published another five books about the Great Wall since then.In 2001, he 17 International Friends of the Great Wall, a(n)

    18 whose efforts are aimed at protecting this 19to the past.

    His next step is to organize exhibitions about the Great Wall as a 20 over the last 400 years.

    The exhibitions are expected to be held in Beijing, London, Paris and Washington DC.