( ( As ( elevation increases ) ) ( , ( ( the pressure ) ( decreases . ) ) ) )
(ROOT (S (PP (IN As) (NP (NN elevation) (NNS increases))) (, ,) (NP (DT the) (NN pressure)) (VP (VBZ decreases)) (. .)))
As elevation 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)) (. .)))