At 9:03, they would see another aircraft strike the World Trade Center.
( ( At 9:03 ) ( , ( they ( ( would ( see ( ( another aircraft ) ( strike ( the ( World ( Trade Center ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN At) (NP (CD 9:03))) (, ,) (NP (PRP they)) (VP (MD would) (VP (VB see) (S (NP (DT another) (NN aircraft)) (VP (VB strike) (NP (DT the) (NNP World) (NNP Trade) (NNP Center)))))) (. .)))
They saw another airplane hit the World Trade Center at 9:03.
( They ( ( saw ( ( another airplane ) ( ( hit ( the ( World ( Trade Center ) ) ) ) ( at 9:03 ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBD saw) (SBAR (S (NP (DT another) (NN airplane)) (VP (VBD hit) (NP (DT the) (NNP World) (NNP Trade) (NNP Center)) (PP (IN at) (NP (CD 9:03))))))) (. .)))