You may come into an empty office after you are told that the school principal is expecting you in her office you may be called at the last minute to come to class after you were told that the class is cancelled for the teacher's illness you may even be given a loving letter, and then find out later it is written by some of your best friends, what is wrong? Nothing, it's just April 1st. We all know April 1st can also be called April fool's Day. But do you know where it came from? Do you know this day used to be a nation's New Year? This is the case in France in sixteenth-century, which, when you think about it, may make more sense, for April is the time when spring returns. And the idea of beginning a year with spring would so easily be understood. The celebration for the New Year is pretty much the same as it is today. People hold and join all sorts of parties, singing and dancing into the late night. Then in 1562, a new calendar was introduced by Pope Gregory for the Christian world. And the New Year began to be celebrated on January first. For any nation, the celebration of New Year is something that can not be replaced by other occasions. And the change of the New Year's date would not be accepted in an easy way. That's also why some people chose not to believe it when hearing the news. So they insist to celebrate New Year on April first, others played tricks on them and called them April fools. Americans play small tricks on friends and strangers in a similar way on the first of April. One commonly-played trick is pointing down to a friend's shoe and saying, your shoelace is untied. And the examples we mentioned at the beginning of our passage is among the limitless ways for children to play tricks on their classmates, friends and so on. Most April fool jokes are in good fun and not meant to harm anyone. The cleverest April fool joke is the one where everyone laughs, especially the person upon whom the joke is played. The examples the author mentions in the first paragraph is to ______ .