He watched the river flow.
( He ( ( watched ( the ( river flow ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD watched) (NP (DT the) (NN river) (NN flow))) (. .)))
The river roared by.
( ( The river ) ( ( roared by ) . ) )
(ROOT (S (NP (DT The) (NN river)) (VP (VBD roared) (PP (IN by))) (. .)))