To determine which theorem accurately completes Reason A ("The measure of angle VQT plus the measure of angle ZRS equals 180 degrees"), we need to analyze the situation with respect to the properties of parallel lines and the angles formed when a transversal intersects those lines.
Given that segments UV and WZ are parallel and intersected by line ST at points Q and R, angles VQT and ZRS are formed.
For angles formed in this configuration, we need the relationship between angles:
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Alternate Interior Angles Theorem: States that if two parallel lines are cut by a transversal, then each pair of alternate interior angles are congruent.
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Corresponding Angles Theorem: States that if two parallel lines are cut by a transversal, then each pair of corresponding angles are congruent.
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Alternate Exterior Angles Theorem: States that if two parallel lines are cut by a transversal, then each pair of alternate exterior angles are congruent.
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Same-Side Interior Angles Theorem: States that if two parallel lines are cut by a transversal, then the same-side interior angles are supplementary (their measures add up to 180 degrees).
Given the angles VQT and ZRS lie on the same side of the transversal ST, and both angles are located inside the parallel lines UV and WZ, they are classified as same-side interior angles.
Therefore, the correct theorem that applies here and completes Reason A is the Same-Side Interior Angles Theorem.