( ( For ( ( water vapor ) ( to ( condense ( in clouds ) ) ) ) ) ( , ( ( particles ( so ( small ( they ( can ( be ( ( seen only ) ( through ( a microscope ) ) ) ) ) ) ) ) ) ( ( must ( be present ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (NP (NN water) (NN vapor)) (SBAR (S (VP (TO to) (VP (VB condense) (PP (IN in) (NP (NNS clouds))))))))) (, ,) (NP (NP (NNS particles)) (ADJP (RB so) (JJ small) (SBAR (S (NP (PRP they)) (VP (MD can) (VP (VB be) (VP (VBN seen) (ADVP (RB only)) (PP (IN through) (NP (DT a) (NN microscope)))))))))) (VP (MD must) (VP (VB be) (ADJP (JJ present)))) (. .)))
For water vapor to condense in clouds, particles so small they can be seen only through a microscope must be present.
(ROOT (S (NP (NNP Water) (NN vapor)) (VP (MD must) (VP (VB lose) (NP (NN heat) (NN energy)) (SBAR (IN before) (S (NP (NNS clouds)) (VP (MD can) (VP (VB form))))))) (. .)))
Water vapor must lose heat energy before clouds can form.