( Power ( ( is ( ( the rate ) ( ( at which ) ( energy ( is transferred ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Power)) (VP (VBZ is) (NP (NP (DT the) (NN rate)) (SBAR (WHPP (IN at) (WHNP (WDT which))) (S (NP (NN energy)) (VP (VBZ is) (VP (VBN transferred))))))) (. .)))
Power is the rate at which energy is transferred.
(ROOT (S (NP (NP (DT The) (NN rate)) (SBAR (IN that) (S (NP (NN energy)) (VP (VBZ is) (VP (VBN released)))))) (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (NN power))))) (. .)))