You ... be late for school.

The best answer is 'shouldn't'. Here's why: * **shouldn't** expresses advice or a recommendation against doing something. It implies that being late for school is undesirable, and the person is being advised to avoid it. * **may not** expresses a possibility that something will not happen. It doesn't give a sense of advice or obligation. * **may** expresses a possibility that something will happen. This makes the sentence sound strange. * **should** expresses advice or obligation to do something. It implies that the person should be late for school, which doesn't make sense. Therefore, the complete sentence is: "You shouldn't be late for school." **Answer:** shouldn't