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 three to four years until it reaches adulthood, and therefore it is
(C) in the Sierra Nevada, mountain yellow-legged tree frogs take three to four years to reach adulthood, thus being
(D) mountain yellow-legged frogs of the Sierra Nevada take three to four years until they reach adulthood, thus
(E) mountain yellow-legged frogs of the Sierra Nevada take three to four years to reach adulthood, and so they are

A

Explanation:

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

Because it is talking about frogs in a comprehensive plural form, this excerpt is the one that best completes and resumes the exposed statement.

(B) it takes the mountain yellow-legged frog of the Sierra Nevada three to four years until it reaches adulthood, and therefore it is:

(C) in the Sierra Nevada, mountain yellow-legged tree frogs take three to four years to reach adulthood, thus being: The statement does not talk about trees, it´s false.

D) mountain yellow-legged frogs of the Sierra Nevada take three to four years until they reach adulthood, thus:   this word is not ending and / or resuming the previous statement.

E) mountain yellow-legged frogs of the Sierra Nevada take three to four years to reach adulthood, and so the:

answer: c

explanation:

reflexive.the third one.