21. _____ is acknowledged to us is that Qian Xuesheng _____ great contributions to our country's agriculture.

  A. As; has done    B. It; does do  C. What; did do     D. What; did did

22. When her father fell into a serious disease, she would sit before the window with her eyes _____ at the street without thinking anything.

  A. stare  B. stared  C. to stare       D. staring