For A, we know that potatoes should be a proper subset of Vegetables, and meat should not overlap with the set of vegetables. This is represented in II. Making A-II a match. 

For B, Law students and Management students are different groups, some portion of which will be men. The Venn-diagram in IV would be the best representation of this. 

For C, Wheat and Maize are different types of Grains, this would be represented by the Venn-diagram in I would be the most appropriate representation of this. 

For D, Oil fruit and Sugar are different entities altogether with no overlap, making the Venn-diagram in III as its best representation. 

Giving the correct matchings as A-II, B-IV, C-II, D-III

Therefore, Option B is the correct answer.