an hour 's worth of actual material 
(ROOT (NP (NP (NP (DT an) (NN hour) (POS 's)) (NN worth)) (PP (IN of) (NP (JJ actual) (NN material)))))
(ROOT (NP (NP (NP (DT ) (NN ) (POS )) (NN )) (PP (IN ) (NP (JJ ) (NN )))))