Your past support of the Challenger program has been critical to its success these last four years.
( ( ( Your ( past support ) ) ( of ( the ( Challenger program ) ) ) ) ( ( has ( ( been critical ) ( ( to ( its success ) ) ( these ( last ( four years ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (PRP$ Your) (JJ past) (NN support)) (PP (IN of) (NP (DT the) (NNP Challenger) (NN program)))) (VP (VBZ has) (VP (VBN been) (ADJP (JJ critical)) (PP (TO to) (NP (PRP$ its) (NN success)) (NP (DT these) (JJ last) (CD four) (NNS years))))) (. .)))
Your past support has been important for the success of the Challenger program
( ( Your ( past support ) ) ( has ( ( been important ) ( for ( ( the success ) ( of ( the ( Challenger program ) ) ) ) ) ) ) )
(ROOT (S (NP (PRP$ Your) (JJ past) (NN support)) (VP (VBZ has) (VP (VBN been) (ADJP (JJ important)) (PP (IN for) (NP (NP (DT the) (NN success)) (PP (IN of) (NP (DT the) (NNP Challenger) (NN program)))))))))