Squares are drawn one inside another. Which figure is the next stage of the pattern?

At each stage a new square is drawn by joining the midpoints of the sides of the smallest square, so it sits tilted at $45^{\circ }$ to the one around it, and the colours take turns: yellow, white, yellow, white. The 4th square is a white tilted one, so the 5th is an upright yellow square joining its midpoints: (a). (b) draws two new squares, (c) colours the new one white, and (d) draws another tilted square instead of joining midpoints.