( ( This ( water vapor ) ) ( then ( ( ( ( ( ( ( ( cools off ) , ) ( ( becomes liquid ) again ) ) , ) and ) then ) ( falls ( as ( ( rain or ) snow ) ) ) ) . ) ) )
(ROOT (S (NP (DT This) (NN water) (NN vapor)) (ADVP (RB then)) (VP (VP (VBZ cools) (PRT (RP off))) (, ,) (VP (VBZ becomes) (NP (NN liquid)) (ADVP (RB again))) (, ,) (CC and) (ADVP (RB then)) (VP (VBZ falls) (PP (IN as) (NP (NN rain) (CC or) (NN snow))))) (. .)))
This water vapor then cools off, becomes liquid again, and then falls as rain or snow.
(ROOT (S (NP (NN Rain)) (VP (VBZ is) (NP (NP (DT an) (NN example)) (PP (IN of) (NP (JJ liquid) (NN water))))) (. .)))