Given two parallel lines, draw two more lines that intersect the two parallel lines, forming various four-sided figures. See the image on the right below for an illustration:

Discuss the properties of the different quadrilaterals formed (e.g., relationships between sides, among angles (acute, obtuse, right, measures, etc.), with diagonals, etc.) . Find as many properties of the quadrilaterals as possible that hold whenever the intersecting lines are moved. What happens when the black lines are no longer parallel?