to look at , listen to , and think about 
(ROOT (S (VP (TO to) (VP (VP (VB look) (PP (IN at))) (, ,) (VP (VB listen) (PP (IN to))) (, ,) (CC and) (VP (VB think) (PP (IN about)))))))
(ROOT (S (VP (TO ) (VP (VP (VB ) (PP (IN ))) (, ) (VP (VB ) (PP (IN ))) (, ) (CC ) (VP (VB ) (PP (IN )))))))