请教OG-137的一个细节

bfghdggf

1. In 1982 the median income for married-couple families with a wage-earning wife was $9,000 more than a family where the husband only was employed.

(A) a family where the husband only

(B) of a family where only the husband

(C) that for families in which only the husband

答案是C没有问题，可是C为什么不用复数husbands而用单数呢？怎么会一个husband在多个familiies里面呢？

himba

要是husband用复数, 会发生歧义: a family have two or more husbands.