going at a rapid pace , occasionally 
(ROOT (S (VP (VBG going) (PP (IN at) (NP (DT a) (JJ rapid) (NN pace))) (, ,) (ADVP (RB occasionally)))))
(ROOT (S (VP (VBG ) (PP (IN ) (NP (DT ) (JJ ) (NN ))) (, ) (ADVP (RB )))))