( ( ( The density ) ( of ( a medium ) ) ) ( also ( ( affects ( ( the speed ) ( of sound ) ) ) . ) ) )
(ROOT (S (NP (NP (DT The) (NN density)) (PP (IN of) (NP (DT a) (NN medium)))) (ADVP (RB also)) (VP (VBZ affects) (NP (NP (DT the) (NN speed)) (PP (IN of) (NP (NN sound))))) (. .)))
The density of a medium also affects the speed of sound.
(ROOT (S (NP (NP (DT The) (NN speed)) (PP (IN of) (NP (NN sound)))) (VP (VBZ depends) (PP (IN on) (NP (NN medium)))) (. .)))
The speed of sound depends on medium.