( ( In ( ( the absence ) ( of ( their medium ) ) ) ) ( , ( ( the ( sound waves ) ) ( ( ( can not ) travel ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NP (DT the) (NN absence)) (PP (IN of) (NP (PRP$ their) (NN medium))))) (, ,) (NP (DT the) (JJ sound) (NNS waves)) (VP (MD can) (RB not) (VP (VB travel))) (. .)))
In the absence of their medium, the sound waves cannot travel.
(ROOT (S (NP (NNP Medium)) (VP (VBZ is) (NP (NP (DT the) (NN matter)) (SBAR (WHPP (IN through) (WHNP (WDT which) (NN sound))) (S (NP (NNS waves)) (VP (VBP travel)))))) (. .)))