听力原文： In the United States, couples usually receive gifts from their relatives and friends when they get married. Sometimes a bride will exchange a gift for something else if she doesn't find it useful. We give gifts to express our good wishes for the marriage, but gifts aren't necessary for the marriage itself. However, in some societies gifts are very important, and the marriage isn't legal without them. One type of gift is called bride service. A young husband must work for his wife's family. He may work for as long as fifteen years or until the third child is bom. Bride service may seem strange to us, but it is necessary in societies where people don't have money or material things to exchange at marriage. (20)