i certainly ca n't recommend it 
(ROOT (S (NP (PRP i)) (ADVP (RB certainly)) (VP (MD ca) (RB n't) (VP (VB recommend) (NP (PRP it))))))
(ROOT (S (NP (PRP )) (ADVP (RB )) (VP (MD ) (RB ) (VP (VB ) (NP (PRP ))))))