On 9/11, the terrorists turned off the transponders on three of the four hijacked aircraft.
( ( On 9/11 ) ( , ( ( the terrorists ) ( ( ( ( turned off ) ( the transponders ) ) ( on ( three ( of ( the ( four ( hijacked aircraft ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN On) (NP (CD 9/11))) (, ,) (NP (DT the) (NNS terrorists)) (VP (VBD turned) (PRT (RP off)) (NP (DT the) (NNS transponders)) (PP (IN on) (NP (NP (CD three)) (PP (IN of) (NP (DT the) (CD four) (JJ hijacked) (NN aircraft)))))) (. .)))
Three of the four hijacked airplanes had their transponders turned off.
( ( Three ( of ( the ( four ( hijacked airplanes ) ) ) ) ) ( ( had ( ( their transponders ) ( turned off ) ) ) . ) )
(ROOT (S (NP (NP (CD Three)) (PP (IN of) (NP (DT the) (CD four) (JJ hijacked) (NNS airplanes)))) (VP (VBD had) (NP (NP (PRP$ their) (NNS transponders)) (VP (VBN turned) (PRT (RP off))))) (. .)))