The correct answer is $\boxed{\text{A. R, R}}$.
The configuration of a chiral center is designated as R or S, depending on the direction of rotation of a Cahn-Ingold-Prelog priority sequence around the chiral center. The priority sequence is determined by the atomic number of the atom bonded to the chiral center, followed by the atomic number of the atom bonded to that atom, and so on. If the rotation is clockwise, the configuration is R. If the rotation is counterclockwise, the configuration is S.
In the reaction shown, the reactant has two chiral centers. The configuration of the first chiral center is R, and the configuration of the second chiral center is R. The product also has two chiral centers. The configuration of the first chiral center is R, and the configuration of the second chiral center is R. Therefore, the configurations of the reactant and the product are both R, R.
Here is a more detailed explanation of each option:
- Option A: R, R. This is the correct answer. The configuration of the reactant and the product are both R, R.
- Option B: R, S. This is incorrect. The configuration of the product is R, R, but the configuration of the reactant is R, S.
- Option C: S, R. This is incorrect. The configuration of the reactant is R, R, but the configuration of the product is S, R.
- Option D: S, S. This is incorrect. The configuration of the reactant is R, R, but the configuration of the product is S, S.