Tales of the supernatural are common in all parts of Britain. In particular, there was (and perhaps still is) a belief in fairies. Not all of these 51are the friendly, people-loving charac-ters that appear in Disney films, and in some folktales they are52and cause much human suf-fering. This is true in the tales about the Changeling. These tell the story of a mother whose ba-by grows 53and pale and has changed so much that it is almost54to the parents. It wasthen55that the fairies had come and stolen the baby away and56the human baby with afairy Changeling. There were many ways to prevent this from happening: hanging a knife over thebaby's head while he slept or covering him with some of his father's clothes were just two of therecommended57. However, hope was not lost even if the baby had been58. In those casesthere was often a way to get the 59baby back. You could60the Changeling on the fire--then it would rise up the chimney, and you would hear the sound of fairies' laughter and soon af-ter you would find your own child safe and sound nearby. 阅读以上短文，回答171-180题。 第51题答案是__________
A.babies B.fairies C.believers D.supermen