function show(atype) {
         var srcElement = document.getElementById(atype);
         if(atype == 'a') {
		    document.getElementById('a').style.display= 'block';
   	    	} else {
			  document.getElementById('a').style.display= 'none';
			  	var selInd = document.forms["search"].length.selectedIndex;
				// get the option object
				var myOption = document.forms["search"].length[selInd];
				// and change into ...:
				myOption.value = "%%";
				
			
			 
       }
  }