---What’s wrong with you, Jack? You look tired.---I ________ to prepare for the final exam last night.
—How are you feeling today? —________ I think I can go to the picnic with you tomorrow.
We should eat _______ fruit and vegetables, but _______ meat. It is good for our health.
—Must we keep the window _______ all the time? —No, you don’t have to.
Smoking can help you relax. But _______ it is also bad for your health.
Some medicine is dangerous for children. Parents should put the medicine in places children can’t _______.