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