function chkValidDatePulldown(year,month,day) {

        var year_index = year.selectedIndex;
        var Year = year[year_index].value;
        var month_index = month.selectedIndex;
        var Month = month[month_index].value;
        var day_index = day.selectedIndex;
        var Day = day[day_index].value;

    if (((Year % 4)==0) && ((Year % 100)!=0) || ((Year % 400)==0)) {
        if (Month == 2 && Day > 29) {
                alert("請選擇一個正確的日子!!");
                year.selectedIndex = 0;
                month.selectedIndex = 0;
                day.selectedIndex = 0;
                return false;
                }
        }

        else if ((Month == 2) && (Day > 28)) {
                alert("請選擇一個正確的日子!!");
                year.selectedIndex = 0;
                month.selectedIndex = 0;
                day.selectedIndex = 0;
                return false;
        }

   if (((Month == 4)||(Month == 6)||(Month == 9)||(Month == 11)) && (Day > 30)) {
                alert("請選擇一個正確的日子!!");
                year.selectedIndex = 0;
                month.selectedIndex = 0;
                day.selectedIndex = 0;
                return false;
        }

} //end chkValidDate