我做到第二步为什么不显示？
<!DOCTYPE HTML>
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>流程控制语句</title>
<script type="text/javascript">
var infos=new Array();
infos[0]=new Array("小A","女",21,"大一");
infos[1]=new Array("小B","男",23,"大三");
infos[2]=new Array("小C","男",24,"大四");
infos[3]=new Array("小D","女",21,"大一");
infos[4]=new Array("小E","女",22,"大四");
infos[5]=new Array("小F","男",21,"大一");
infos[6]=new Array("小G","女",22,"大二");
infos[7]=new Array("小H","女",20,"大三");
infos[8]=new Array("小I","女",20,"大一");
infos[9]=new Array("小J","男",20,"大三");
//第一步把之前的数据写成一个数组的形式,定义变量为 infos
for(var i=0;i<9;i++){
if(infos[i][3]="大一"){
document.write(infos[i][0]+"<br/>");
}
}
//第一次筛选，找出都是大一的信息
