( ( The ( water droplets ) ) ( then ( ( form ( a cloud ) ) . ) ) )
(ROOT (S (NP (DT The) (NN water) (NNS droplets)) (ADVP (RB then)) (VP (VBP form) (NP (DT a) (NN cloud))) (. .)))
The water droplets then form a cloud.
(ROOT (S (NP (NNS Clouds)) (VP (VBP are) (VP (VBN formed) (PP (IN from) (NP (NN water) (NNS droplets))))) (. .)))