If $A \subseteq B$, then $A \cup B$ equals

If $A \subseteq B$, then $A \cup B$ equals
  1. $B$
  2. $A$
  3. $\emptyset$
  4. $U$

Solution

All of $A$ is already in $B$, so the union is $B$.

Asked in: MH-SSC-9

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