( People ( ( have ( to ( stop ( polluting ( the earth ) ) ) ) ) . ) )
(ROOT (S (NP (NNS People)) (VP (VBP have) (S (VP (TO to) (VP (VB stop) (NP (VBG polluting) (NP (DT the) (NN earth))))))) (. .)))
People have to stop polluting the earth.
(ROOT (S (NP (NNS People)) (VP (VBD stopped) (S (VP (VBG adding) (NP (NN lead)) (PP (TO to) (NP (NP (NN gasoline)) (PP (RB because) (IN of) (NP (JJ environmental) (NN pollution)))))))) (. .)))