By fifty a married man or woman was probably to have suffered widowhood, and ________ half his or her contemporaries: in contrast to a mere twentieth today.
句意：与今天二十岁的小年轻做比较，到五十岁的时候，已婚的男性或者女性可能已经遭遇丧偶守 寡，也会丧失一半的同龄人。根据句中的was以及by fifty的提醒，可知时态应该用过去将来完成时。因此， 本题的正确答案为A。