I couldn't have done it.
( I ( ( ( could n't ) ( have ( done it ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (MD could) (RB n't) (VP (VB have) (VP (VBN done) (NP (PRP it))))) (. .)))
I couldn't have done it.
( I ( ( ( could n't ) ( have ( done it ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (MD could) (RB n't) (VP (VB have) (VP (VBN done) (NP (PRP it))))) (. .)))