(S (S (BASENP (DT A) (JJ full) (NN investigation)) (VP (VBZ is) (VP (VBG being) (VP (VBN conducted) (PP (IN into) (SBAR (WHNP (WP what)) (S (VP (VBD caused) (BASENP (DT the) (NN crash)))))))))) (PERIOD .))