function part2() { 
var part2 = document.getElementById('part2'); 
if ( part2.className == 'hidden' ) { 
part2.className = 'visible'; 
} else { 
part2.className = 'hidden'; 
} 
} 

function partb() { 
var partb = document.getElementById('partb'); 
if ( partb.className == 'hidden' ) { 
partb.className = 'visible'; 
} else { 
partb.className = 'hidden'; 
} 
}