function light(){
??????? var trs = document.getElementsByTagName("tr");
??????? for(var i=1;i<trs.length;i++){
???????? trs[i].onmouseover = function(){

?????? ??? ???? this.style.backgroundColor ="#f2f2f2";//這個this是指什么，trs[i]嗎？它是什么意思？？

?? ??? ???? }
?? ??? ??? ?trs[i].onmouseout = function(){
?? ??? ??? ??? ?this.style.backgroundColor ="#fff";
?? ??? ??? ?}
??????? }
??? }