( PROCEDURE ( ( ( A ( dramatic illustration ) ) ( of ( ( the variation ) ( of ( ( the speed ) ( of ( sound ( with ( ( the density ) ( of ( a gas ) ) ) ) ) ) ) ) ) ) ) ( ( is ( performed ( by ( ( ( breathing ( ( ( a ( low density ) ) and ) ( a ( high ( density gas ) ) ) ) ) and ) ( talking ( as ( ( the gas ) ( is ( expelled ( from ( the lungs ) ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (ADVP (RB PROCEDURE)) (NP (NP (DT A) (JJ dramatic) (NN illustration)) (PP (IN of) (NP (NP (DT the) (NN variation)) (PP (IN of) (NP (NP (DT the) (NN speed)) (PP (IN of) (NP (NP (NN sound)) (PP (IN with) (NP (NP (DT the) (NN density)) (PP (IN of) (NP (DT a) (NN gas)))))))))))) (VP (VBZ is) (VP (VBN performed) (PP (IN by) (S (VP (VP (VBG breathing) (NP (NP (DT a) (JJ low) (NN density)) (CC and) (NP (DT a) (JJ high) (NN density) (NN gas)))) (CC and) (VP (VBG talking) (SBAR (IN as) (S (NP (DT the) (NN gas)) (VP (VBZ is) (VP (VBN expelled) (PP (IN from) (NP (DT the) (NNS lungs))))))))))))) (. .)))
PROCEDURE A dramatic illustration of the variation of the speed of sound with the density of a gas is performed by breathing a low density and a high density gas and talking as the gas is expelled from the lungs.
(ROOT (S (NP (NNS Gases)) (VP (VBP have) (NP (DT the) (JJS lowest) (NN density))) (. .)))