Use the figure and flowchart proof to answer the question:
segments uv and wz are parallel segments that intersect line st at points q and r, respectively
points s, q, r, and t all lie on the same line; given. arrows are drawn from this statement to the following three statements. statement 1: the measure of angle sqt equals 180 degrees; reason 1: definition of a straight angle. statement 2: the measure of angle sqv plus the measure of angle vqt equals the measure of angle sqt; reason 2: angle addition postulate. statement 3: the measure of angle sqv plus the measure of angle vqt equals 180 degrees; reason 3: substitution property of equality. lines uv and wz are parallel; given. an arrow is drawn from this statement to the following statements. statement 4: the measure of angle vqt plus the measure of angle zrs equals 180 degrees; reason a. statement 5: the measure of angle sqv plus the measure of angle vqt equals the measure of angle vqt plus the measure of angle zrs; reason b. an arrow also points from statement 3 to statement 5. an arrow from statement 5 points to the following statements. statement 6: the measure of angle sqv plus the measure of angle vqt minus the measure of angle vqt equals the measure of angle vqt plus the measure of angle zrs minus the measure of angle vqt, the measure of angle sqv equals the measure of angle zrs; reason c. statement 7: the measure of angle sqv is congruent to the measure of angle zrs; definition of congruency.
which theorem accurately completes reason a?
a) alternate interior angles theorem
b) corresponding angles theorem
c) alternate exterior angles theorem
d) same-side interior angles theorem