我们发现在习题教学中存在两种比较普遍的现象:一是选题随意,目的不强;二是就题论题,提炼不够.这些现象直接导致了教学中的无用功过多,同时也是以题目覆盖为主要特征的题海战术盛行的一个重要原因. We find that there are two common phenomena in the exercise teaching: one is the random choice, the other is not strong enough; the other is the problem, which is not enough for refinement. These phenomena directly lead to excessive uselessness in teaching, As the main feature of the sea is an important reason for the prevalence of tactics.