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# If $A$ and $B$ are two sets such that $A \subset B$,then what is $A\cup B$?

$\begin{array}{1 1}(A)\;A&(B)\;B\\(C)\;AB&(D)\;BA\end{array}$

Since A is a subset of B,therefore every element of set A is contained in the set B and hence $A\cup B=B$
Hence (B) is the correct answer.