21．After the war,a lot of serious problems___ and the price of food____by 20%.
A. rise ,rise B. rose , arose C. arose ,rose D. raised, aroused
22．When the traffic lights turned green, the police_____ the child to cross the street.
A. signaled B. signed C. sight D. sigh
23. We will never forget Mr.Smith,______ help we have made great progress.
A. his B. with whom C. who D. with whose
