Final answer:
The correct postulate or theorem for the given statement is the Vertical Angles Theorem.
Step-by-step explanation:
To prove that angle MRO + angle MRS equals angle SRO, we can use the Vertical Angles Theorem. The Vertical Angles Theorem states that when two lines intersect, the pairs of opposite angles formed are congruent. In this case, angle MRS and angle SRO are opposite angles formed by the intersecting lines MR and RS. Since angle MRS is equal to angle MRO, by the Vertical Angles Theorem, angle SRO must also be equal to angle MRS and angle MRO.