's good enough to be the purr 
(ROOT (VP (VBZ 's) (ADJP (JJ good) (RB enough) (S (VP (TO to) (VP (VB be) (NP (DT the) (NN purr))))))))
(ROOT (VP (VBZ ) (ADJP (JJ ) (RB ) (S (VP (TO ) (VP (VB ) (NP (DT ) (NN ))))))))