—Mr. Wang, must I come again to clean the window on Sunday morning?—No, you _____ . I have asked others to do it.

It ___________last night, for the ground is wet outside.

We can eat in the dining hall. But we _______ eat in the classroom.

(2010·辽宁高考)Doctors say that exercise is important for health, but it ________ be regular exercise.

If you spend the spring sneezing, take a look at your plate. Some foods _____ make allergies worse.