In parallelogram ABCD, diagonal AC is drawn. Which reason best justifies why area(△ABC)=area(△CDA)?
(a) Both triangles lie on the same base AC and between the same parallels, so their areas are equal.
(b) The triangles have equal corresponding angles and share side AC, making them congruent by ASA.
(c) △ABC and △CDA are congruent by SAS.
(d) The diagonal AC bisects the angles of the parallelogram, making the triangles similar and therefore equal in area.