3. Let $a, b, c$ be distinct natural numbers, and $a b^{2} c^{3}=$ 675. Then the maximum value of $a+b+c$ is ( ).
(A) 50
(B) 79
(C) 76
(D) 78
3. B.
$$
\text { Sol } \begin{array}{l}
a b^{2} c^{3}=675=3^{3} 5^{2} \\
\quad=5^{2} \cdot 1^{2} \cdot 3^{3}=3^{3} \cdot 5^{2} \cdot 1^{3} \\
\quad=\left(5^{2} \cdot 3\right) \cdot 3^{2} \cdot 1^{3}=3 \cdot(3 \cdot 5)^{2} \cdot 1^{3} .
\end{array}
$$
$$
\text { Therefore } a+b+c=75+3+1=79 \text {. }
$$