Five years.
( Five ( years . ) )
(ROOT (NP (CD Five) (NNS years) (. .)))
It's been five years.
( It ( ( 's ( been ( five years ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ 's) (VP (VBN been) (NP (CD five) (NNS years)))) (. .)))