GMAT Sentence Correction (SC) | Unlike frogs that metamorphose from tadpoles into adults

Unlike frogs that metamorphose from tadpoles into adults within a one-year period,it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are restricted to deeper bodies of water that do not dry up in summer or freeze solid in winter.

(A) it takes three to four years for the mountain yellow-legged frog of the Sierra Nevada to reach adulthood, and so they are
(B) it takes the mountain yellow-legged frog of the Sierra Nevada