Hi, I need some help in solving this question:

"Draw any quadrilateral, find the midpoints of its sides and join consecutive midpoints to form an inner quadrilateral. Make a hypothesis about the inner quad. Use deductive geometry to prove your hypothesis is true."

This is what I got so far:

The quadrilateral inside seems to be always a parallelogram no matter what shape the outside quadrilateral is like.

The hard part is that i don't how to use deductive geometry to prove this. (I do know some deductive geometry, but I just don't know where to start.)