First, multiple-choice questions (4 points for each question, ***48 points)
12. As shown in the figure, in the right-angle ABCD, AB=4, BC=, point E is a moving point on the broken line A-D-C (point E does not coincide with point A), and point P on point A-D-C is the symmetrical point of point A about BE. During the movement of point E, the position of point E that makes △PCB an isosceles triangle is * *.
A.2 B.3 C.4 D.5
Answer: c