requiring a great deal of thought 
(ROOT (S (VP (VBG requiring) (NP (NP (DT a) (JJ great) (NN deal)) (PP (IN of) (NP (NN thought)))))))
(ROOT (S (VP (VBG ) (NP (NP (DT ) (JJ ) (NN )) (PP (IN ) (NP (NN )))))))