I.单选题
21. Beijing is addressing air pollution on _______ larger scale and with more investment to ensure _______ blue skies than it did for the Olympics.
A. a; 不填; B. a; the C. the; the D. the; 不填;
22. —Thanks for your help, but can you do me one more favor, please?
— _______, Sir. What’s it then?
A. Just a minute B. My pleasure C. That’s right D. At your service
23. _______ the source of the bird flu virus, the identities, background and living conditions of existing patients will be investigated.
A. To determine B. Determining C. Determined D. Having determined
