( ( ( Water vapor ) ( remains ( ( ( in ( ( the atmosphere ) ( for ( several days ) ) ) ) and ) ( through ( combination ( of circumstances ) ) ) ) ) ) ( , ( changes ( ( ( back ( to ( ( the ( liquid state ) ) ( through ( a process ) ) ) ) ) ( ( called condensation ) ( to ( form clouds ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (NNP Water) (NN vapor)) (VP (VBZ remains) (PP (PP (IN in) (NP (NP (DT the) (NN atmosphere)) (PP (IN for) (NP (JJ several) (NNS days))))) (CC and) (PP (IN through) (NP (NP (NN combination)) (PP (IN of) (NP (NNS circumstances)))))))) (, ,) (NP (NNS changes)) (VP (ADVP (RB back) (PP (TO to) (NP (NP (DT the) (JJ liquid) (NN state)) (PP (IN through) (NP (DT a) (NN process)))))) (VBD called) (NP (NN condensation)) (S (VP (TO to) (VP (VB form) (NP (NNS clouds)))))) (. .)))
Water vapor remains in the atmosphere for several days and through combination of circumstances, changes back to the liquid state through a process called condensation to form clouds.
(ROOT (S (NP (NNP Condensation)) (VP (MD must) (VP (VB occur) (PP (IN for) (NP (NNS clouds))) (S (VP (TO to) (VP (VB form)))))) (. .)))