function changeBg(div_id,pic){
document.getElementById(div_id).style.backgroundImage="url('images/"+pic+"')";
}



function menu_on(num){
document.getElementById(num).style.visibility='visible';
}

function hide_all () {
document.getElementById('p1').style.visibility='hidden';
document.getElementById('p3').style.visibility='hidden';
document.getElementById('p4').style.visibility='hidden';
document.getElementById('p5').style.visibility='hidden';
document.getElementById('p6').style.visibility='hidden';
}