function tab(ss){
a=['t1','t2','t3','t4','t5'];
b=['s1','s2','s3','s4','s5'];
for(i=0;i<a.length;i++){
document.getElementById(a[i]).className="a1";
document.getElementById(b[i]).style.display="none";
}

ks=document.getElementById(a[ss-1]);
ds=document.getElementById(b[ss-1]);

if(ds==null) return;
if(ks==null) return;

ks.className="a2";
ds.style.display="block";
}