从四个选项中，选出可以填入空白处的最佳选项，
21
．—Good morning , May I help you ?
—Oh, thank you．I’m just looking around．
—_______________．
A．Thanks for coming to see me ． B．How are you feeling today?
C．I’ll write you a check right now． D．Take your time , then．
22．What shall we use for power when all the oil in the world has ______?
A．given out B．put out C．held up D．used up
