#### Answer

$B$

#### Work Step by Step

RECALL:
(1) $\cup$ represents union of sets, which is the set that contains the combined elements of the sets involved.
(2) $\emptyset$ is the empty set, which has no elements.
Since $\emptyset$ is empty, then the union of the two given sets will just be the non-empty set $B$.
Thus,
$\color{blue}{B \cup \emptyset = B}$