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

(N/A) Let $U = N$ be the set of natural numbers.
Given set $A = \{ x : x \text{ is an even natural number} \}$.
The complement of set $A$ is denoted by $A^\prime$ or $A^c$.
$A^\prime = U - A = \{ x : x \in N \text{ and } x \notin A \}$.
Since $N$ consists of all natural numbers,removing even natural numbers leaves only odd natural numbers.
Therefore,$A^\prime = \{ x : x \text{ is an odd natural number} \}$.