( ( As ( the ( altitude increases ) ) ) ( , ( ( the pressure ) ( decreases . ) ) ) )
(ROOT (S (PP (IN As) (NP (DT the) (NN altitude) (NNS increases))) (, ,) (NP (DT the) (NN pressure)) (VP (VBZ decreases)) (. .)))
As the altitude increases, the pressure decreases.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN gas) (NNS particles)) (VP (VB heat) (PRT (RP up))))) (, ,) (NP (NN pressure)) (VP (VBP increase)) (. .)))