's hard to resist his enthusiasm 
(ROOT (S (VP (VBZ 's) (ADJP (JJ hard)) (S (VP (TO to) (VP (VB resist) (NP (PRP$ his) (NN enthusiasm))))))))
(ROOT (S (VP (VBZ ) (ADJP (JJ )) (S (VP (TO ) (VP (VB ) (NP (PRP$ ) (NN ))))))))