Chemistry stoichiometry question

What will be the molar concentration (M) of a solution of Sr(OH)2 which has a pH
equal to 12?
A) 0.1 M
B) 1 x 10-2 M
C) 1 x 10-12 M
D) 2 M
E) 5 x 10-3M

BTW (E) is the answer and i am not sure how to solve it…would be helpful if someone helped me out to solve it.