When parallel lines are cut by a transversal, which of these statements must be true about the measures of vertical angles?
They are not equal to each other, because one vertical angle is not supplementary to the other.
They are equal to each other, because one vertical angle is a reflection of the other.
They are not equal to each other, because one vertical angle is not a reflection of the other.
They are equal to each other, because one vertical angle is supplementary to the other.