从A、B、C、D四个选项中，选出k^s*5#u可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. Obama, ________ president of the USA, won ________ Nobel Prize for Peace in 2009.
A. 不填；a 不填；the C. a；the D. the；a
22. --May I speak to Professor White, please?
--Sorry, he isn’t in. This is his assistant speaking. Can I help you?
A. Oh, you can Oh, it’s a pity
C. I hope to see him soon D. I should think so
23. The Chinese government has made ________ a goal to increase peasants’ income.
A. it this C. that D. one