How did general lee’s smaller army defeat mcclellan’s force and keep union troops out of richmond

The way that General Lee’s smaller army manage to defeat McClellan’s force and keep Union troops out of Richmond is: b) Lee took advantage of McClellan's cautious style 
Knowing McCellan's style, General lee keep ordering unrelenting assaults to the  McClellan's forces, making him became distracted and losing a lot of his men at the same time.