Answer:Triangles BPA and DPC are congruent is used to prove that ABCD is a parallelogram.
Explanation:Here, we have given a quadrilateral ABCD in which diagonals AC and BD bisect each other.
If P is a an intersection point of these diagonals
Then we can say that, AP=PC and BP=PD ( by the property of bisecting)
So, In quadrilateral ABCD,
Let us take two triangles, and .
Here, AP=PC
BP=PD,
( vertically opposite angles.)
So, By SAS postulate,
Thus AB=CD ( CPCT).
Similarly, we can prove,
Thus, AD=BC (CPCT).
Similarly, we can get the pair of congruent opposite angle for this quadrilateral ABCD.
Therefore, quadrilateral ABCD is a parallelogram.
Note: With help of other options we can not prove quadrilateral ABCD is a parallelogram.