i want to be a model student. what shall i do?
　　i should be polite. i should study hard. i should capful and helpful. i should walk in the corridors. i should throw rubbish in the bin. i should be quiet in the library.
　　i shouldn”t walk and run on the grass. i shouldn”t throw rubbish on the floor. i shouldn”t run in the corridors. i shouldn”t fight. i shouldn”t be noisy in the library.
　　how about you?