By will, D left Blackacre to A for life, remainder to B. Ds residuary estate was left to S, Ds spouse. Both A and B effectively, under Section 2518 disclaimed their interests in Blackacre.

A) How may this affect the marital deduction for Ds estate?

B) Is the answer the same if C is the residuary legatee under Ds will, but, after Ds death, A and B effectively direct the transfer of Blackacre to S?

C) Under what circumstances (and with what effect) might a surviving spouse be likely to disclaim an interest in property left to the surviving spouse?