从A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. ―It takes _________ patience and skill to be a teacher.
―Well, at least I’m not impatient man.
A. the; a B. the; a C. 不填; a D. 不填; an
22. —How did you manage to get such a nice old painting?
—Quite _______.
A. by accidents B. by a chance C. by accident D. by incident
23. Mind your ______; thank your friend when you leave the party.
A. advice B. ways C. manners
