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 only one challenge.
( ( These ( top dogs ) ) ( ( face ( only ( one challenge ) ) ) . ) )
(ROOT (S (NP (DT These) (JJ top) (NNS dogs)) (VP (VBP face) (NP (RB only) (CD one) (NN challenge))) (. .)))