In conditional sentences, "would you" is used to express hypothetical or unreal situations. This sentence presents a hypothetical scenario (car breaking down), so the appropriate modal verb is "would." "Will" is used for real future situations, which doesn't fit here.
- Option (a) "will you" is incorrect as it suggests a real situation rather than a hypothetical one.
- Option (c) "may you" is incorrect because "may" is used for permission, not hypothetical situations.
- Option (d) "did you" is incorrect because it doesn't align with the conditional structure.
Therefore, the correct answer is "would you."