All the hijackers had assigned seats in first class, and they seem to have used them.
( ( ( ( ( ( All ( the hijackers ) ) ( had ( assigned ( seats ( in ( first class ) ) ) ) ) ) , ) and ) ( they ( seem ( to ( have ( used them ) ) ) ) ) ) . )
(ROOT (S (S (NP (PDT All) (DT the) (NNS hijackers)) (VP (VBD had) (VP (VBN assigned) (NP (NP (NNS seats)) (PP (IN in) (NP (JJ first) (NN class))))))) (, ,) (CC and) (S (NP (PRP they)) (VP (VBP seem) (S (VP (TO to) (VP (VB have) (VP (VBN used) (NP (PRP them)))))))) (. .)))
The hijackers sat in the front of the plane.
( ( The hijackers ) ( ( sat ( in ( ( the front ) ( of ( the plane ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS hijackers)) (VP (VBD sat) (PP (IN in) (NP (NP (DT the) (NN front)) (PP (IN of) (NP (DT the) (NN plane)))))) (. .)))