5. (3 points) In the arithmetic expression shown in the figure, each letter represents a non-zero digit, and different letters represent different digits. The minimum value of the sum is ( )
$$
\begin{array}{r}
A B C \\
+\quad D E F \\
\hline H I J
\end{array}
$$
A. 369
B. 396
C. 459
D. 549
【Analysis】According to the problem, the highest digit of the sum is at least 3. If $H=3$, then $A$ and $D$ are 1 and 2 respectively, leaving the numbers $4, 5, 6, 7, 8, 9$. No matter how the units and tens digits are arranged, there will be a carry, so $H$ cannot be 3. Therefore, $H$ can only be at least 4, with $A$ and $D$ still being 1 and 2. The remaining numbers are $3, 5, 6, 7, 8, 9$. It is clear that when adding, there will be a carry from the tens place to the next higher place. Since each digit represents a different number, after calculation and experimentation, we can get: $73+86=159$, so the smallest sum in this problem is $173+286=459$. According to this, the answer can be chosen.

【Solution】According to the analysis of the problem, we get:
$$
\begin{array}{r}
173 \\
+286 \\
\hline 459
\end{array}
$$

Answer: The smallest sum is 459.
Therefore, the correct choice is: $C$.