听力题 Imagine this: you wake up each morning to find your sister lying beside you, to get dressed and tie your shoes. You use one hand and she uses another. You do everything else together too, even sitting on the same chair at lunch and riding on the same bicycle. That''s what life is like for the six-year-old Betty and Abby. Like most twins, the two girls look very much alike. But unlike most twins, Betty and Abby share parts of the same body. Twins like Betty and Abby are rare. Only about forty sets are born in the United States each year. Few survive as long as Betty and Abby. That''s because twins often share vital organs like a heart or brain. These shared organs are often badly shaped and may not be strong enough to support both twins. But Betty and Abby each has her own head, heart and stomach which function normally. The girls share three or four lungs, which provide plenty of oxygen for both twins. Most of their completely shared organs lie below the waist. Betty and Abby live relatively normal lives. They attend a regular school and each does her own school work. They prefer to do some projects together, though, for example, to cut out paper dolls. One twin holds the paper, while the other uses the scissors. But sometimes the girls don''t want to do the same thing. For example, sometimes they want to play with different toys. What do they do, then? "We toss the coin," says Abby.