21．While income worry israther common problem of the aged, loneliness is another problem thataged parents may face
A．a; 不填 B．the；不填 C．a：the D．the，：the
22．The control and prevention of H1Nl is a big to China as well as the whole world．
A，surprise B．challenge C．reaction D．threat
23．Although many heroes’family members were killed in“5. 12”Wen Chuan earthquake, they choked back their sobs to rescue other survivorstheir personal safety．
A．instead of B．because of
C．regardless of D．in case of