Question

Marvin reflected this trapezoid over a line, but only 2 of the vertices changed position. Which line could Marvin have used for the reflection?

Answer 1

He chose a line that was collinear with one of the trapezoids parallel sides. A trapezoid has only one pair of sides that are parallel. If Marvin chose a line that was collinear with on of these sides, then the result would be only two points changing position as the other two points would be on the line of transformation.