What theorem is dynamically being illustrated in the applet below? (Feel free to move the white points anywhere you'd like!)
[color=#000000][b]Theorem:[/b][/color][br]The [color=#000000][b]midpoints[/b][/color] of the 4 sides of any quadrilateral always form [color=#000000][b]vertices of a parallelogram[/b][/color]. [br](We know that from the theorem that states if a quadrilateral has both pairs of opposite sides congruent, then that quadrilateral is a parallelogram.)