Marlene can conclude that the measure of the vertical angles must be equal. The correct option is the first option - that the measure of the angles must be equal.
Vertically opposite angles
From the question, we are to determine what Marlene can conclude from the observation. That is, we are to determine the correct statement
From the given information,
"Marlene noticed that when a pair of parallel lines was cut by a transversal, two particular vertical angles were reflection of each other"
If two angles are reflection of each other, then the angle must be equal.
From Marlene's observation, the two vertical angles are reflection of each other.
This means the vertical angles must be equal.
Hence, Marlene can conclude that the measure of the vertical angles must be equal. The correct option is the first option - that the measure of the angles must be equal.
Learn more on Vertical angles here: https://brainly.com/question/1673457
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