( Condensation ( ( is ( when ( clouds form ) ) ) . ) )
(ROOT (S (NP (NNP Condensation)) (VP (VBZ is) (SBAR (WHADVP (WRB when)) (S (NP (NNS clouds)) (VP (VBP form))))) (. .)))
Condensation is when clouds form.
(ROOT (S (NP (NNP Condensation)) (VP (MD must) (VP (VB occur) (PP (IN for) (NP (NNS clouds))) (S (VP (TO to) (VP (VB form)))))) (. .)))