All understood the plane had been hijacked.
( All ( ( understood ( ( the plane ) ( had ( been hijacked ) ) ) ) . ) )
(ROOT (S (NP (DT All)) (VP (VBD understood) (SBAR (S (NP (DT the) (NN plane)) (VP (VBD had) (VP (VBN been) (VP (VBN hijacked))))))) (. .)))
Most people didn't realize that the plane had been hijacked. 
( ( Most people ) ( ( ( did n't ) ( realize ( that ( ( the plane ) ( had ( been hijacked ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJS Most) (NNS people)) (VP (VBD did) (RB n't) (VP (VB realize) (SBAR (IN that) (S (NP (DT the) (NN plane)) (VP (VBD had) (VP (VBN been) (VP (VBN hijacked)))))))) (. .)))