Question

S is a subset within a universal set, U.

If S = {x, y, 4, 9, ?}, which could describe U?

U = {keys on a keyboard}
U = {letters}
U = {numbers}
U = {punctuation marks}

Answer 1

U = {keys on a keyboard}

Reason: S contains letters (x, y), numbers (4, 9) and a punctuation mark (?). Only the set of keyboard keys includes all those types.