建于1831年的伦敦桥在1962年被拆掉，然而1971年这座桥出现在了美国加州。

　　In 1962，London Bridge was falling down.Built in 1831，the bridge couldn't handle the ever­increasing flow of traffic across the Thames River.The British government decided to put the bridge up for sale，and Robert McCulloch，founder of Lake Havasu City，Arizona，submitted the winning bid of 2,460,000.

　　The bridge was taken down，and each stone was numbered.Everything was shipped 10,000 miles to Long Beach，California，and then trucked to Lake Havasu City.Reconstruction began on September 23,1968, with a ceremony including the Lord Mayor of London，who laid the cornerstone.On October 10,1971，the bridge was rebuilt.

　　To reach the bridge from I­40，we recommend going south on Arizona Highway 95，then turn left (east) on Mesquite Avenue.Turn right on Lake Havasu Avenue N．and then right again on McCulloch Boulevard N．to drive over the bridge.

　　Just after turning onto McCulloch Boulevard N．， you'll cross over Arizona Highway 95.Before you reach the actual London Bridge，it's best to turn left into the small parking lot near the London Bridge Resort.It's an easy walk along the lower edge of the bridge to the promenade(散步) for photos.

　　Once you walk west under the bridge，you'll see a walkway which leads up to the London Bridge visitors' center where there are some historical photos and other information about the bridge and other attractions and places of interest within about a 100­mile radius(半径) of Lake Havasu City.

　　Lake Havasu City，which got its start as an Army Air Corps rest camp during World War Ⅱ，now has over 1,000 businesses，two newspapers and a college.Remember that the next time a man comes up to you and offers to sell you a used bridge!

根据上面短文回答下列问题

1．Why was London Bridge falling down?