window.onload = function() {
   var ImgSwitch = document.getElementById("mainph");//‰æ‘œ‚ÌID
   var myMonth=new Date();
   Seasons = myMonth.getMonth() + 1;
       if(Seasons>=3 && Seasons<6){
           ImgSwitch.className="spring";//�t
       }else if(Seasons>=6 && Seasons<9){
           ImgSwitch.className="summer";//‰Ä
       }else if(Seasons>=9 && Seasons<12){
           ImgSwitch.className="autumn";//�H
       }else if(Seasons==12 || Seasons<=2){
           ImgSwitch.className="winter";//“~
       }
   }