21. Why not buy him _______ MP4 as_______ birthday present since he likes music?
A. an； the B. the； the C. an； a D. a； a
22．It rained for two weeks on end, completely _____ our holiday．
A．to ruin B．ruining C．ruined D．ruin
23. William found it increasingly difficult to read，for his eyesight was beginning to .
A. disappear B. fall C. fail D. damage
