Her voice was doubtful.
( ( Her voice ) ( ( was doubtful ) . ) )
(ROOT (S (NP (PRP$ Her) (NN voice)) (VP (VBD was) (ADJP (JJ doubtful))) (. .)))
She was doubtful because the plan did not seem very good.
( She ( ( ( was doubtful ) ( because ( ( the plan ) ( ( did not ) ( seem ( very good ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP She)) (VP (VBD was) (ADJP (JJ doubtful)) (SBAR (IN because) (S (NP (DT the) (NN plan)) (VP (VBD did) (RB not) (VP (VB seem) (ADJP (RB very) (JJ good))))))) (. .)))