If $A$ and $B$ are two sets,then $A \cap (A \cup B)'$ is equal to

Taking the set of natural numbers as the universal set,write down the complement of the following set:
$A = \{ x : x \text{ is an odd natural number} \}$

Taking the set of natural numbers as the universal set,write down the complement of the following set:
$A = \{x: 2x + 5 = 9\}$

If $A$ is any set,then:

Taking the set of natural numbers as the universal set,write down the complement of the following set:
$A = \{ x : x \text{ is a perfect square} \}$

Let $U = \{1, 2, 3, 4, 5, 6, 7, 8, 9\}$,$A = \{1, 2, 3, 4\}$,$B = \{2, 4, 6, 8\}$,and $C = \{3, 4, 5, 6\}$. Find $(B - C)'$.