Which of the following statements is always true when a diagonal is drawn in a parallelogram?
(a) The diagonal divides the parallelogram into two triangles of equal area but not necessarily congruent.
(b) The diagonal divides the parallelogram into two triangles that are always similar but not congruent.
(c) The diagonal divides the parallelogram into two congruent triangles.
(d) The diagonal divides the parallelogram into two isosceles triangles.