what 's missing from this material 
(ROOT (SBAR (WHNP (WP what)) (S (VP (VBZ 's) (VP (VBG missing) (PP (IN from) (NP (DT this) (NN material))))))))
(ROOT (SBAR (WHNP (WP )) (S (VP (VBZ ) (VP (VBG ) (PP (IN ) (NP (DT ) (NN ))))))))