Answer:- A) U= { keys on a keyboard}
Explanation:-
- A set is a well defined collection of objects.
- A Universal set is the set containing all objects and all other sets are subsets of the universal set. It is denoted by 'U'.
Given set : S = {x,y,4,9,?}
Clearly it contains numbers (4,9), alphabets(x,y) and punctuation mark(?).
Thus the universal set of the given set must contain all of them.
Thus U={keys on a keyboard}
