Answer
Force of attraction, greatest to least: B=C, A, D.
Work Step by Step
$$F_{A}= G \frac{M m}{d^{2}}$$
$$F_{B}= G \frac{(2M) m}{d^{2}} = 2 \times F_{A}$$
$$F_{C}= G \frac{M (2m)}{d^{2}} = 2 \times F_{A}$$
$$F_{D}= G \frac{M (2m)}{(2 d)^{2}} = 0.5 \times F_{A}$$
