should be doing a lot of things , but does n't . 
(ROOT (S (VP (MD should) (VP (VB be) (VP (VBG doing) (NP (NP (DT a) (NN lot)) (PP (IN of) (NP (NNS things))))))) (, ,) (CC but) (VP (VBZ does) (RB n't)) (. .)))
(ROOT (S (VP (MD ) (VP (VB ) (VP (VBG ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (NNS ))))))) (, ) (CC ) (VP (VBZ ) (RB )) (. )))