Three pintail ducks from North America turned up in widely separated parts of the world. One duck was taken near Cali, Colombia, South America; one in Japan; and the third along the Dart River in England. The South American hunter was told that his duck had come from North Dakota. The Japanese scientists learned that their bird had been on a National Wildlife Refuge in New Mexico. The English sportsman found that his pintail, just 21 days before, had been seen in Labrador, some 2,200 miles across the Atlantic. How did these people know their ducks had come from North America?

It really isn't such a mystery as it might seem. On the leg of each duck the hunter had found an aluminum band. The band carried a number and a request that the finder of the band report to the Bird Banding Laboratory, Washington, D.C. Each hunter did exactly that.

Q. Underline the sentence which supports the conclusion drawn in question No. 2.