The correct answer is B (57%). The minimum margin requirement (MMR) is calculated as the reciprocal of the maximum leverage ratio (MLR), i.e., MMR = 1 / MLR. Given a maximum leverage ratio of 1.75, the minimum margin requirement is 1 / 1.75 = 57%. Option A (43%) is incorrect as it represents a miscalculation, and Option C (75%) is incorrect as it misinterprets the relationship between the leverage ratio and the margin requirement.