( ( A ( nuclear reactor ) ) ( ( is ( a ( device ( to ( ( ( initiate and ) control ) ( a ( sustained ( nuclear ( chain reaction ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ nuclear) (NN reactor)) (VP (VBZ is) (NP (DT a) (NN device) (S (VP (TO to) (VP (VB initiate) (CC and) (VB control) (NP (DT a) (JJ sustained) (JJ nuclear) (NN chain) (NN reaction))))))) (. .)))
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction.
(ROOT (S (NP (NNP Control) (NNS rods)) (VP (VBP play) (NP (NP (DT an) (JJ important) (NN role)) (PP (IN in) (NP (NP (DT the) (NN modulation)) (PP (IN of) (NP (DT the) (JJ nuclear) (NN chain) (NN reaction))))))) (. .)))