If you still have a headache, you’d better ________ a doctor

Do you have a pen?I want _____ a letter.   

He often practice          the piano in his room.

---What should we do to fight A/H1N1 flu?---We should wash hands often, avoid ______ to crowded places and so on.

My parents told me try ______on Christmas Eve because Santa Clause may come and send me some gifts.