By writing 3 to the right of a three-digit natural number, a four-digit number A is obtained, and by writing 2 to the left of the same number, a four-digit number B is obtained.
If $\mathrm{A} + \mathrm{B} = 9967$, what is the sum of the digits of the three-digit number?
A) 12
B) 9
C) 15
D) 13
E) 11