21. Britain was the first country in the world to have ____ free health care system paid for by ____ government.

A. /, a    B. a, the    C. /, the    D. a, a

22.   Kind and patient, my first English teacher, Mrs Li, explains grammar ____ clearly, especially in this opening class, that even I can understand it.

Avery    B. too    C. so    D. rather