21. I consider it. honor to hear you speak highly of me.
A. / B. an C. the D. a
22. Because of the earthquake， some parts of the countryside are only by helicopter.
A. available B. appropriate C. accessible D. achievable
23. I failed again in the examination and only then ___ how much time I had wasted.
A. I realized B. I had realized C. did I realize D. had I realized
