the extent to which it succeeds is impressive . 
(ROOT (S (NP (NP (DT the) (NN extent)) (SBAR (WHPP (IN to) (WHNP (WDT which))) (S (NP (PRP it)) (VP (VBZ succeeds))))) (VP (VBZ is) (ADJP (JJ impressive))) (. .)))
(ROOT (S (NP (NP (DT ) (NN )) (SBAR (WHPP (IN ) (WHNP (WDT ))) (S (NP (PRP )) (VP (VBZ ))))) (VP (VBZ ) (ADJP (JJ ))) (. )))