I just can't remember.
( I ( just ( ( ( ca n't ) remember ) . ) ) )
(ROOT (S (NP (PRP I)) (ADVP (RB just)) (VP (MD ca) (RB n't) (VP (VB remember))) (. .)))
I knew it was something I have seen before.
( I ( ( knew ( it ( was ( something ( I ( have ( seen before ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBD knew) (SBAR (S (NP (PRP it)) (VP (VBD was) (NP (NP (NN something)) (SBAR (S (NP (PRP I)) (VP (VBP have) (VP (VBN seen) (ADVP (RB before))))))))))) (. .)))