( But ( , ( ( if ( you ( change ( ( ( the speed ) ( of ( ( ( a wave ) and ) ( the frequency ) ) ) ) ( stays ( the same ) ) ) ) ) ) ( , ( ( the wavelength ) ( ( must change ) . ) ) ) ) ) )
(ROOT (S (CC But) (, ,) (SBAR (IN if) (S (NP (PRP you)) (VP (VBP change) (SBAR (S (NP (NP (DT the) (NN speed)) (PP (IN of) (NP (NP (DT a) (NN wave)) (CC and) (NP (DT the) (NN frequency))))) (VP (VBZ stays) (NP (DT the) (JJ same)))))))) (, ,) (NP (DT the) (NN wavelength)) (VP (MD must) (VP (VB change))) (. .)))
But, if you change the speed of a wave and the frequency stays the same, the wavelength must change.
(ROOT (S (NP (NP (DT The) (NN product)) (PP (IN of) (NP (NP (NP (DT a) (NN wave) (POS 's)) (NN wavelength)) (CC and) (NP (PRP$ its) (NN frequency))))) (VP (VBZ is) (NP (PRP$ its) (NN speed))) (. .)))