( ( Ultrasound waves ) ( ( are ( produced ( by ( ( oscillating crystals ) ( at ( ( a frequency ) ( that ( is ( inaudible ( to ( the ( human ear ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Ultrasound) (NNS waves)) (VP (VBP are) (VP (VBN produced) (PP (IN by) (S (VP (VBG oscillating) (NP (NNS crystals)) (PP (IN at) (NP (NP (DT a) (NN frequency)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADJP (JJ inaudible) (PP (TO to) (NP (DT the) (JJ human) (NN ear)))))))))))))) (. .)))
Ultrasound waves are produced by oscillating crystals at a frequency that is inaudible to the human ear.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (NN sound)) (SBAR (WHNP (WDT that)) (S (VP (VBZ has) (S (NP (DT a) (NN wave) (NN frequency)) (ADJP (JJR higher) (SBAR (IN than) (S (NP (DT the) (JJ human) (NN ear)) (VP (MD can) (VP (VB detect) (NP (NN ultrasound))))))))))))) (. .)))