function checkQuantity() {
    var q1, q2, q3, q4;
    if ($('ddlAmount1'))
        q1 = $('ddlAmount1').options[$('ddlAmount1').selectedIndex].value;
    else
        q1 = '-';

    if ($('ddlAmount2'))
        q2 = $('ddlAmount2').options[$('ddlAmount2').selectedIndex].value;
    else
        q2 = '-';

    if ($('ddlAmount3'))
        q3 = $('ddlAmount3').options[$('ddlAmount3').selectedIndex].value;
    else
        q3 = '-';

    if ($('ddlAmount4'))
        q4 = $('ddlAmount4').options[$('ddlAmount4').selectedIndex].value;
    else
        q4 = '-';

    if ($('imgBtnPost')) {

        var img = $('imgBtnPost');
        if (q1 + q2 + q3 + q4 == '----') {
            img.src = img_dis_src;
            img.style.cursor = "default";
            img.disabled = true;
        } else {
            img.src = img_en_src;
            img.style.cursor = "pointer";
            img.disabled = false;
        }
    }
}