Let's go through them.
A. The bases of an isosceles triangle are congruent. FALSE
The sides that's aren't the bases are congruent, but the bases (parallel top and bottom) are generally different.
B. Rectangle is equiangular quadrilateral. TRUE All the angles of a rectangle are right angles, so all equal.
C. Base angles are of isosceles trapezoid are congruent. TRUE
D. Rhombus diagonals are perpendicular bisectors of each other. TRUE
Answer: A