at best , i 'm afraid . 
(ROOT (S (PP (IN at) (NP (JJS best))) (, ,) (NP (PRP i)) (VP (VBP 'm) (ADJP (JJ afraid))) (. .)))
(ROOT (S (PP (IN ) (NP (JJS ))) (, ) (NP (PRP )) (VP (VBP ) (ADJP (JJ ))) (. )))