How is Y related to Z ?
Statement I. Z and A are children of E who is wife of Y.
Statement II. S's sister Y is married to Z's father.
If the data either in statement I alone or in statement II alone are sufficient to answer the question
From I, we conclude that Y is the child of D who is wife of X i.e. Xis Y's father. From II, X is married to Y's father. This implies that X is Y's mother.