21．¬¬¬After ________ series of unsuccessful attempts, he has finally passed ________driving test．
A．/;the B． a; the C． the; a D． /;a
22．—My God! I’m getting late again，what will my boss say?
—Try to keep ________; we will think of an excuse．
A． silent B． calm C． still D． quiet
23．1. Every evening after dinner, if not _________from work, I will spend some time walking my dog.
A. being tired B. tiring C. tired D. to be tired
