( ( As ( ( ( air pressure ) ( -LRB- ( ( ( the number ) ( of molecules ) ) -RRB- ) ) ) ( is reduced ) ) ) ( , ( it ( ( is ( easier ( to ( boil water ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (NP (NN air) (NN pressure)) (PRN (-LRB- -LRB-) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS molecules)))) (-RRB- -RRB-))) (VP (VBZ is) (VP (VBN reduced))))) (, ,) (NP (PRP it)) (VP (VBZ is) (ADJP (ADJP (JJR easier)) (PP (TO to) (NP (NN boil) (NN water))))) (. .)))
As air pressure (the number of molecules) is reduced, it is easier to boil water.
(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))))) (. .)))