April 1 every year is April Fool's Day. It is the happiest day for the people in western countries. On April 1, you can tell a lie, make a joke to others, or cheat them, but they will not be angry with you.
If it were April 1 today, you could tell your good friends, "I hear there is an important exam tomorrow. Don't tell others about it". And the people who believe you are called April Fools.
This custom started in France during the 16th century. It spread to England in the 18th century, and then to the United States.
【参考译文】
每年4月1日是愚人节，它是西方国家人们最开心的日子。在4月1日，你可以跟别人说谎、开玩笑，或者骗他们，而他们并不与你生气。
假如今天是4月1日，你可以告诉你的好朋友：“我听说明天有一次重要的考试。可别告诉别人!”而相信你的花的人被称为愚人。
这个风俗是在16世纪在法国开始的，在18世纪传到英国，后来又传到美国。
