var elem1=document.forms[0].placeKb1;
var elem2=document.forms[0].placeKb2;
var elem3=document.forms[0].placeKb3;
var elem2Value=elem2.value;
var elem3Value=elem3.value;
var i;
var j;
if (t=1) {
//有第1个下拉的值,确定第2个下拉列表
elem2.length = 1; //清空下拉列表
j=0;
for (i=0; i<arrPlaceKb12List.length; i++) {
if (elem1.value==arrPlaceKb12List[i][0] || elem1.value=="") {
//方法1
//elem2.options.add(new Option(arrPlaceKb12List[i][2], arrPlaceKb12List[i][1]));