I pick B .
Although she had signed a pledge of abstinence while being an adolescent. Frances Willard was 35 years
old before she chose to become a temperance activist.
(A) while being an adolescent - signed becoz she was adolescent.
(B) while in adolescence - signed when she was adolescent
(C) at the time of her being adolescent - bit wordy
(D) as being in adolescence - signed becoz she was adolescent
(E) as an adolescent - not sure.. but it tells the state in which she signed and not the time frame. Like I did it as a child vs. i did it while I was a child
Not sure how correct the reasonings are.