To determine which pair of angles is supplementary when lines \( s \) and \( t \) are parallel, let's analyze the angle relationships:
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Consecutive Exterior Angles: Angles \( \angle A \) and \( \angle D \) are consecutive exterior angles. However, consecutive exterior angles are not necessarily supplementary when lines are parallel; they are congruent instead.
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Corresponding Angles: Angles \( \angle A \) and \( \angle B \) are corresponding angles. Corresponding angles are congruent when the lines are parallel, so they are not supplementary.
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Consecutive Interior Angles: Angles \( \angle B \) and \( \angle G \) are consecutive interior angles. When lines are parallel, consecutive interior angles are supplementary (they add up to 180 degrees).
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Linear Pair: Angles \( \angle G \) and \( \angle D \) can be a linear pair if they lie on a straight line. Linear pairs are always supplementary, but without knowing the exact configuration, we can't confirm if this is the case.
Based on this analysis, the correct choice for a pair of supplementary angles when lines \( s \) and \( t \) are parallel is:
\( \angle B \) and \( \angle G \) because they are consecutive interior angles.
This is the only pair that is guaranteed to be supplementary due to the properties of parallel lines and transversal angles.