Once a boy often made trouble. His mother gave him many nails . She told him to hammer(,)one in the garden fence  every time he lost his patience and fought with someone. The first day he hammered 27 nails. In the following weeks he learned how to control himself better and the number of nails hammered became smaller and smaller. He learned it was easier to control himself than to hammer nails. The day finally came when he didn't hammer any nails. He went to tell his mother about it. Then his mother told him to pull off a nail from the fence each time he didn't lose his patience. After some days he told his mother that all the nails had been pulled off, so she took him to the fence and said to him, "You've behaved well, but look at all the holes in the fence. The fence will never be again like it was before. When you fight with someone, you leave wounds in him like these. The trouble may be over, but the wounds will always be there." So, learn to control yourself before you hammer the nail in the fence. Try not to leave any holes in your past. The boy used to   _  .
be polite be impatient be careless be friendly to others