( ( The beats ) ( ( ( are ( ( a result ) ( of ( ( the interference ) ( of ( the ( two ( sound waves ) ) ) ) ) ) ) ) . ) -RRB- ) )
(ROOT (S (NP (DT The) (NNS beats)) (VP (VBP are) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (NP (DT the) (NN interference)) (PP (IN of) (NP (DT the) (CD two) (JJ sound) (NNS waves))))))) (. .) (-RRB- -RRB-)))
The beats are a result of the interference of the two sound waves.)
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS waves)) (PP (IN of) (NP (CD two) (JJ different) (NNS frequencies)))) (VP (VBP interfere)))) (, ,) (NP (NN beating)) (VP (VBZ occurs)) (. .)))