If all members of X are also members of Y, and some members of Y are not in X, what is the relationship between X and Y?

• A. X is a subset of Y
• B. X and Y are disjoint
• C. Y is a subset of X
• D. They are identical

Answer: (A)

Subset relationship: If every element of X is also an element of Y, then X is contained in Y. Because Y has some elements not in X, the containment is proper, so X is a proper subset of Y. The other options don’t fit: disjoint would mean no overlap, which isn’t true here; identical would mean no difference between the sets, which there is; and Y being a subset of X would require all of Y to be in X, contradicting that Y has elements outside X.