There are two challengers to these top dogs.
( There ( ( are ( ( two challengers ) ( to ( these ( top dogs ) ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD two) (NNS challengers)) (PP (TO to) (NP (DT these) (JJ top) (NNS dogs))))) (. .)))
These top dogs face two challenges.
( ( These ( top dogs ) ) ( ( face ( two challenges ) ) . ) )
(ROOT (S (NP (DT These) (JJ top) (NNS dogs)) (VP (VBP face) (NP (CD two) (NNS challenges))) (. .)))