function address(){

    var provinces= ["北京市","天津市","河北省","河南省"];

    var province = document.getElementById("province");

    var i=0;

    for(;i<provinces.length;i++){

         province.options.add(new Option(provinces[i]));

    }

}

function linkage(){

     var cities = ["朝阳区","西城区","石家庄","邯郸市","西青区","武清区","郑州市","开封市"]

    var city = document.getElementById("city");

    var province = document.getElementById("province");

    city.options.length = 0;

    if(province.value=="北京市"){

        selectAdd(city,cities,0);

        selectAdd(city,cities,1);

    }else if(province.value=="河北省"){

        selectAdd(city,cities,2);

        selectAdd(city,cities,3);

    }else if(province.value=="天津市"){

        selectAdd(city,cities,4);

        selectAdd(city,cities,5);

    }else if(province.value=="河南省"){

         selectAdd(city,cities,6);

        selectAdd(city,cities,7);

    }

}

function selectAdd(obj,name,value){

/*请在此补充代码*/  

obj.options.add(new Option(name[value]));

}