On October 31st, dozens of children dressed in costumes（节日服装）knock on their neighbors' doors and yell Trick or Treat when the door opens. Pirates and princesses, ghosts and popular heroes of the day all hold bags open to catch the candy or other goodies that the neighbors drop in. As they give each child a treat the neighbors exclaim over the costumes and try to guess who is under the masks.Since the 800's November 1st is a religious holiday known as All Saints' Day（万圣节）。 The Mass that was said on this day was called Allhallowmas. The evening before became known as All Hakkiw e'en, or Halloween. Like some other American celebrations, its origins lie in both pre-Christian and Christian customs.October 31 st was the eve of the Celtic（凯尔特人的）new year. The Celts were the ancestors of the present-day Irish, Welsh and Scottish people. On this day