一个经典的羊车游戏，有三个门，有一个后面有车，2个后面有羊，当你做选择时，主持人将其中一个有羊的门公布，你可以选择不改变，随机选择或改选另一个门，这个例子对mvc模式有很好的理解-Sheep a classic car games, there are three doors, one behind a car, two behind the sheep, when you choose, the host will be one of the doors have announced the