var n=Math.floor(Math.random()*2+2);
            if(n==2){
                var pic="2.png";
            }else if(n==3){
                var pic="3.png";
            }
document.write("<img src=img/'+pic+'>");

var n=Math.floor(Math.random()*2+2);
            
            imgs[current].src="images/n+'.png'";

就是替换当前出现的图片   这个改怎么整