catch it ... if you can ! 
(ROOT (S (VP (VB catch) (NP (PRP it)) (, ...) (SBAR (IN if) (S (NP (PRP you)) (VP (MD can))))) (. !)))
(ROOT (S (VP (VB ) (NP (PRP )) (, ) (SBAR (IN ) (S (NP (PRP )) (VP (MD ))))) (. )))