To complete the figure which option is required:

The correct answer is Option (1) → 

Going round the square clockwise (top left, top right, bottom right, bottom left), the black half of the circle turns through 90° clockwise at each step: right half, bottom half, left half, top half. Its slanting line, from the bottom-left corner to the top-right corner, completes the diamond formed by the four slanting lines.