One's deceased father grind mathematics proposition change once every five years because:

1, the number of propositional groups is limited. Asking the same group of people to make a proposition for a long time will not only reduce the quality of the proposition, but also let the candidates find the rule of the proposer's problem by studying the real question, thus affecting the difficulty of the test questions.

2. After changing the proposition group, the new proposer will put forward the proposition according to his own style and thinking, which can add some difficulty to the candidates and test their true level.