( ( Radio waves ) ( ( are ( received ( at ( varying frequencies ) ) ) ) . ) )
(ROOT (S (NP (NNP Radio) (NNS waves)) (VP (VBP are) (VP (VBN received) (PP (IN at) (NP (VBG varying) (NNS frequencies))))) (. .)))
Radio waves are received at varying frequencies.
(ROOT (S (NP (NNP Am) (NN radio) (NNS waves)) (VP (VBP exist) (PRT (RP in)) (NP (DT the) (ADJP (QP (CD 540) (TO to) (CD 1600))) (NN khz) (NN frequency) (NN range))) (. .)))