it was difficult
( it ( was difficult ) )
(ROOT (S (NP (PRP it)) (VP (VBD was) (ADJP (JJ difficult)))))
It was challenging to fight him.
( It ( ( was ( challenging ( to ( fight him ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBD was) (VP (VBG challenging) (S (VP (TO to) (VP (VB fight) (NP (PRP him))))))) (. .)))