Because the weekly conferences serve a genuine educational function, the spending limit confines the sponsorship, and the rotation among industry members limits the exposure of any particular industry representative, option B is the preferable alternative.
Refusing industry sponsorship (option A) is always acceptable, and setting a limit on Melissima's spending for the meals it provides (option D) is also acceptable. There may be some reason to avoid option D, nonetheless. Because of the frequency of the conferences, the weekly modest meal will accumulate to become a substantial gift.
Without a spending limit, there is no way to ensure that the gifts from Melissima or any other industry representative will be modest, and so options C and E should be avoided.
Preferable: Option B
Acceptable: Options A and D
Avoid: Options C and E