( ( The humidity ) ( ( becomes ( rain ( when ( ( the water ) ( ( changes phase ) ( back ( into liquid ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN humidity)) (VP (VBZ becomes) (NP (NP (NN rain)) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NN water)) (VP (VBZ changes) (NP (NN phase)) (ADVP (RB back) (PP (IN into) (ADJP (JJ liquid))))))))) (. .)))
The humidity becomes rain when the water changes phase back into liquid.
(ROOT (S (NP (NN Rain)) (VP (VBZ is) (NP (NP (DT an) (NN example)) (PP (IN of) (NP (JJ liquid) (NN water))))) (. .)))