(S (S (BASENP (PRP It)) (VP (VP (VP (VBZ is) (ADVP (RB still))) (ADJP (JJ unknown) (PP (TO to) (BASENP (NNP NASA) (NNS officials))))) (SBAR (WHNP (WP what)) (S (VP (VBD caused) (S (BASENP (DT the) (NN sensor)) (VP (TO to) (VP (VB become) (ADJP (JJ defective)))))))))) (PERIOD .))