//ロールオーバー
function clearAll(){
    document.getElementById("studentvoice").src="images/index/btn_studentvoice.gif";
}
function changeImg1(){document.getElementById("studentvoice").src="images/index/btn_studentvoice_on.gif";}
function backImg1(){document.getElementById("studentvoice").src="images/index/btn_studentvoice.gif";}