The actions that prove that the quadrilateral is a parallelogram are:
Quadrilaterals are polygons that have four sides and four corners
Parallelograms are quadrilaterals that have parallel and congruent opposite sides
For the quadrilateral to be a parallelogram, then the opposite sides must be congruent.
This can be proved using the distance formula
Also, for the quadrilateral to be a parallelogram, then the opposite sides must be parallel.
This can be proved using the slope formula
Hence, the possible actions are (a) and (b)
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