We've got to think.
( We ( ( 've ( got ( to think ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP 've) (VP (VBN got) (S (VP (TO to) (VP (VB think)))))) (. .)))
We can think.
( We ( ( can think ) . ) )
(ROOT (S (NP (PRP We)) (VP (MD can) (VP (VB think))) (. .)))