most substantial feature for some time 
(ROOT (NP (NP (ADJP (RBS most) (JJ substantial)) (NN feature)) (PP (IN for) (NP (DT some) (NN time)))))
(ROOT (NP (NP (ADJP (RBS ) (JJ )) (NN )) (PP (IN ) (NP (DT ) (NN )))))