By will, D left Blackacre to A for life, remainder to B. D's residuary estate was left to S, D's spouse. Both A and B effectively, under Section 2518 disclaimed their interests in Blackacre. a.) How may this affect the marital deduction for D's estate? b.) Is the answer the same if C is the residuary legatee under D's will, but, after D's 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?