21.Do you believe＿idea that the world will be at__end?
A.an,the B.the,an C.the,the D.an,an
22.The professor,for__was hard in the past,still works hard in his seventies
A.whom life B.whose life C.who life D.he lives
23.___back from America that year__the girl he would like to marry.
A.It was until he came, that he met B.Not until he came, he met
C.Not util he came, did he meet D.Not until did he come, he met
