21．The boss wanted an assistant with _____ knowledge of French and _____ work experience．
A．the; a B．不填；the C．a; 不填 D．the; 不填
22．_____ is expected that it will be fine tomorrow, when we can do some outdoor activities．
A．As B．It C．That D．Which
23．—Has your father returned from Africa yet?
—Yes, but he _____ here for only three days before his company sent him to Australia．
A．was B．has been C．will be D．would be
