The correct answer is A.
Every column contains two shapes. The left column contains a triangle and a circle, the middle column contains a circle and a square, and the right column contains a square and a triangle. Down the column, one shape increases in size while another shape decreases in size. Take a look at the right column. The triangle becomes progressively smaller as the square becomes progressively bigger. Therefore, the answer-option will have a small triangle inside a large square. Eliminate answer-option D, since it is missing a large square.
Additionally, in each row, each shape of the same size is of a different color. In the bottom row, there is a small, white circle and a small, black square. Therefore, the answer-option will contain a small, gray triangle. You can eliminate answer-options B and E. Furthermore, in the bottom row, there is a large, black triangle, and a large gray, circle. Therefore, the answer-option will contain a large, white square. Eliminate answer-option C and you are left with answer-option A as the correct answer.