Use the multinomial theorem to show that, for positive integers $n$ and $t$.
$$
t^{n}=\sum\left(\begin{array}{c}
n \\
n_{1} n_{2} \cdots n_{t}
\end{array}\right)
$$,
where the summation extends over all nonnegative integral solutions $n_{1}, n_{2}, \ldots, n_{t}$ of $n_{1}+n_{2}+\cdots+n_{t}=n$.