function hideImage() {
     var numlinks = 4;
     var linkTag;
     var linkActive
     var content;
     for (i=1; i<=numlinks; i++) {
         linkTag = "link" + i + "a";
         content = "content" + i;
         document.getElementById(content).style.display = "none";
         linkActive = document.getElementById(linkTag);
         linkActive.parentNode.className = "";
     }
}
function showImage(which) {
     hideImage();
     var linkTag2 = "link" + which + "a";
     var linkActive
     var content2 = "content" + which;
     document.getElementById(content2).style.display = "block";
     linkActive = document.getElementById(linkTag2);
     linkActive.parentNode.className = "active";
}