Find the union of each of the following pairs of sets:
$A = \{1, 2, 3\}, B = \varnothing$

For any two sets $A$ and $B$, $A-(A-B)$ equals

If $A = \{3, 5, 7, 9, 11\}$,$B = \{7, 9, 11, 13\}$,$C = \{11, 13, 15\}$ and $D = \{15, 17\}$; find $B \cap C$.

If $A = \{1, 2, 3, 4\}$,$B = \{3, 4, 5, 6\}$,$C = \{5, 6, 7, 8\}$,and $D = \{7, 8, 9, 10\}$,find $A \cup B \cup D$.

If $A = \{ x : x \text{ is a natural number} \}$,$B = \{ x : x \text{ is an even natural number} \}$,$C = \{ x : x \text{ is an odd natural number} \}$,and $D = \{ x : x \text{ is a prime number} \}$,find $B \cap D$.

Draw the appropriate Venn diagram for the following set operation: $A^{\prime} \cap B^{\prime}$.