( ( ( The decrease ) ( in ( ( the number ) ( of ( gas molecules ) ) ) ) ) ( ( ( ( lowers ( the pressure ) ) ( inside ( the bottle ) ) ) ( because ( pressure ( is ( directly ( proportional ( to ( ( the number ) ( of ( gas molecules ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN decrease)) (PP (IN in) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NN gas) (NNS molecules)))))) (VP (VBZ lowers) (NP (DT the) (NN pressure)) (PP (IN inside) (NP (DT the) (NN bottle))) (SBAR (IN because) (S (NP (NN pressure)) (VP (VBZ is) (ADJP (RB directly) (JJ proportional) (PP (TO to) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NN gas) (NNS molecules)))))))))) (. .)))
The decrease in the number of gas molecules lowers the pressure inside the bottle because pressure is directly proportional to the number of gas molecules.
(ROOT (S (S (VP (VBG Reducing) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS molecules)) (PP (IN in) (NP (DT a) (JJ rigid) (NN container)))))))) (VP (VBZ causes) (NP (NN pressure)) (S (VP (TO to) (VP (VB decrease))))) (. .)))