Answer:
A. Show that the diagonals form two congruent triangles using the definition of a rhombus and geometric properties. Then, use CPCTC (corresponding parts of congruent triangles are congruent) to show that the opposite interior angles are bisected.
Explanation:
Answer choice A is the only one that applies specifically to a rhombus.
The other answer choices are true of triangles and vertical angles in general. They do not relate specifically to the problem at hand.