= Solution
{c}
Use the convention that $W_n$ is the <wheel graph> with rim $C_n$ and one additional hub; the assumption $n\geq3$ gives the rim at least three vertices. The rim needs two colours for even $n$ and three for odd $n$. Since the hub is adjacent to every rim vertex, its colour must be a new one. These lower bounds are attained by properly colouring the rim and adding that extra colour. Thus
$$
\boxed{\chi(W_n)=\begin{cases}3,&n\text{ even},\\4,&n\text{ odd}.\end{cases}}
$$
If a convention indexes a wheel by its total number of vertices instead, replace the rim size $n$ by $n-1$ in this formula.
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