Sister-in-law is

Concept

In English kinship terminology, ‘sister-in-law’ is not a single fixed relation. It is a general label applied to more than one type of female in-law: a spouse’s sister, and a sibling’s wife.

Application

Applying this here: a husband’s sister is one accepted sister-in-law relation; a wife’s sister is also one; and a brother’s wife is also one. Because the term legitimately covers all three relations rather than being restricted to a single one, no individual relation by itself is the complete answer.

• Husband’s sister

• Wife’s sister

• Brother’s wife

Cross-check

Ruling out the possibility that none of the relations qualify: husband’s sister, wife’s sister, and brother’s wife are all textbook-correct uses of ‘sister-in-law’, so at least one — in fact all three — of the listed relations is valid, which rules out ‘none of the above’ as well.

So the correct choice is the option indicating that more than one of the listed relations is valid.