20.It is not who is right but what is right ____ is of importance

A　 which　　　　　 B it　　　　　 C that　　　　 D this

19. All possible means ____. However , nothing can ____ him dying of lung cancer.

A. has tried; stop　　 B. have been tried;keep　　 C. has been tried; stop　 D have been tried;stop

18. ---Do you mind if I open the window？

---_________ I feel a bit cold.

A .Of course not　　　　 B. I would rather you didn’t　　 C. Go ahead　　　 D. Why not?