function hideAll(){
tag = document.getElementsByTagName("div");
	for(x=0;x<tag.length; x++){
		if(tag[x].getAttribute('id').indexOf("course_") != -1){
			tag[x].style.display = "none";
		}
	}
}

function show(id){
el = document.getElementById('course_' + id.value);
		hideAll();
		el.style.display = "block";
}