Answer:
The bottom left picture is the answer. It contains 4 equally sized parts and only has 1 shaded part, so that's 1 shaded part / 4 parts, or 1/4. The top left picture have 5 parts instead of 4 (1/5), the parts in the top right picture aren't equally sized, and the bottom right picture has 2 parts shaded instead of 1 (1/2)
Hope this helps!