A, E - Incorrect: The comparison doubly likely is awkward compared to the equality form twice as likely.
B - Incorrect: The pronoun it doesn't have a clear antecedent, and this construction is unidiomatic.
D - Incorrect: Than is not used in the equality form with as. The correct form is: as + adj/adv + as, for example twice as likely as instead of twice as likely than.
C - Correct: The equality form used here is correct: as + adj/adv + as .