7-6的编程问题，不懂为什么最后是new Option(name[i])这个直接填i怎么不行呢？

function address(){
    /*请在此补充代码*/
    var sf=document.getElementById("sf");
    var sq=document.getElementById("sq");
    var arrsf=["北京市","天津市","河北省","河南省"];
    var arrsq=["朝阳区","西城区","石家庄","邯郸市","西青区","武清区","郑州市","开封市"];
    selectAdd(sf,arrsf,arrsf);
    selectAdd(sq,arrsq,arrsf);
}
function selectAdd(obj,name,value){
	/*请在此补充代码*/  
	for(var i in name){
	    obj.options.add(new Option(name[i]));
	}
}