( ( Reactive behavior ) ( ( requires ( only ( reflex action ) ) ) . ) )
(ROOT (S (NP (JJ Reactive) (NN behavior)) (VP (VBZ requires) (NP (RB only) (JJ reflex) (NN action))) (. .)))
Reactive behavior requires only reflex action.
(ROOT (S (NP (NNP Reflex) (NNS behaviors)) (VP (VBP are) (NP (NP (DT the) (RB only) (JJ innate) (NNS behaviors)) (PP (IN in) (NP (NNS humans))))) (. .)))