That was Robert Frost.
( That ( ( was ( Robert Frost ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBD was) (NP (NNP Robert) (NNP Frost))) (. .)))
Robert Frost was a poet.
( ( Robert Frost ) ( ( was ( a poet ) ) . ) )
(ROOT (S (NP (NNP Robert) (NNP Frost)) (VP (VBD was) (NP (DT a) (NN poet))) (. .)))