The details of what happened on the morning of September 11 are complex, but they play out a simple theme.
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(ROOT (S (S (NP (NP (DT The) (NNS details)) (PP (IN of) (SBAR (WHNP (WP what)) (S (VP (VBD happened) (PP (IN on) (NP (NP (DT the) (NN morning)) (PP (IN of) (NP (NNP September) (CD 11)))))))))) (VP (VBP are) (ADJP (JJ complex)))) (, ,) (CC but) (S (NP (PRP they)) (VP (VBP play) (PRT (RP out)) (NP (DT a) (JJ simple) (NN theme)))) (. .)))
The details of what happened on the morning of September 11 are simple and straightforward.
( ( ( The details ) ( of ( what ( happened ( on ( ( the morning ) ( of ( September 11 ) ) ) ) ) ) ) ) ( ( are ( ( simple and ) straightforward ) ) . ) )
(ROOT (S (NP (NP (DT The) (NNS details)) (PP (IN of) (SBAR (WHNP (WP what)) (S (VP (VBD happened) (PP (IN on) (NP (NP (DT the) (NN morning)) (PP (IN of) (NP (NNP September) (CD 11)))))))))) (VP (VBP are) (ADJP (JJ simple) (CC and) (JJ straightforward))) (. .)))