function changeMc(a,b,n){
 document.getElementById(a).style.display = "block";
 document.getElementById(b).style.display = "none";
 var c=document.getElementById('b_bbs_b_title').getElementsByTagName('a');
 for(i=0;i<=a.length;i++)
 {
 
 	c[i].className=(i==n)?"hover":"";
 }
}