( It ( ( ( is not ) ( ( the ( basic energy ) ) ( that ( keeps ( ( the string ) vibrating ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (RB not) (NP (NP (DT the) (JJ basic) (NN energy)) (SBAR (WHNP (WDT that)) (S (VP (VBZ keeps) (NP (NP (DT the) (NN string)) (VP (VBG vibrating)))))))) (. .)))
It is not the basic energy that keeps the string vibrating.
(ROOT (S (PP (IN Like) (NP (NP (DT the) (NNS strings)) (PP (IN of) (NP (NN cello))))) (, ,) (NP (NP (NN anything)) (SBAR (WHNP (WDT that)) (S (VP (VBZ vibrates))))) (VP (VBZ produces) (NP (NP (NNS waves)) (PP (IN of) (NP (NN energy))))) (. .)))