从每小题所给的四个选项（A、B、C和D）中，选出可以填入空白处的最佳选项。
21. _____ Chinese basketball player Yao Ming will probably return to the NBA if he can recover from _____ earlier injury.
A. 不填; an B. The; 不填 C. A; an D. The; the
22. —Mr. Smith _____ in Russia for 10 years.
—No wonder he can speak Russian fluently and now teaches Russian in a Chinese college.
A. had stayed B. has stayed C. stayed D. stays
