( ( Air temperature ) ( ( remains constant ) . ) )
(ROOT (S (NP (NNP Air) (NN temperature)) (VP (VBZ remains) (ADJP (JJ constant))) (. .)))
Air temperature remains constant .
(ROOT (S (PP (IN During) (NP (NN phase) (NN change))) (, ,) (NP (NP (DT the) (NN temperature)) (PP (IN of) (NP (DT a) (NN system)))) (VP (VBZ remains) (ADJP (JJ constant))) (. .)))