The figure at the bottom shows a square ABCD and an equilateral triangle DPC: Nick makes the chart shown below to prove that triangle APD is congruent to triangle BPC:

Statements Justifications
In triangles APD and BPC; AP = PB P is the vertex of the equilateral triangle
In triangles APD and BPC; AD = BC Sides of square ABCD are equal
In triangles APD and BPC; angle ADP = angle BCP Angle ADC = angle BCD = 90° and angle ADP = angle BCP = 90° − 60° = 30°
Triangles APD and BPC are congruent SAS postulate

What is the error in Nick's proof? (1 point)

Select one:
a. He uses the SAS postulate instead of AAS postulate to prove the triangles congruent.
b. He assumes that AP = PB because P is the vertex of the equilateral triangle.
c. He uses the SAS postulate instead of SSS postulate to prove the triangles congruent.
d. He writes the measure of angles ADP and BCP as 30° instead of 45°.