(S (S (BASENP (NNP NASA)) (VP (VBZ has) (VP (VBN said) (SBAR (IN that) (S (BASENP (JJ preliminary) (NNS investigations)) (VP (VBP show) (SBAR (IN that) (S (BASENP (NNP Discovery)) (VP (VBZ is) (ADJP (JJ safe) (S (VP (TO to) (VP (VB fly) (ADVP (RB home))))))))))))))) (PERIOD .))