that stubbornly refused to gel 
(ROOT (SBAR (WHNP (DT that)) (S (ADVP (RB stubbornly)) (VP (VBD refused) (S (VP (TO to) (VP (VB gel))))))))
(ROOT (SBAR (WHNP (DT )) (S (ADVP (RB )) (VP (VBD ) (S (VP (TO ) (VP (VB ))))))))