21．When a giraffe（长颈鹿） has ______ drink, it has to stand with its front legs wide open apart in order to reach ______ water．
A．/; / B．a; the C．the; / D．/ ; the
22．Clean water is ______ necessary than fresh air to [\people living in big cities．
A．no more B．not more C．no less D．not less
