We are given the limit:
\[
L = \lim_{x \to 0} \frac{ax^3 + bx^2 + cx}{3x^2}
\]
Step 1: Simplify the expression
Factor out \( x \) from the numerator:
\[
L = \lim_{x \to 0} \frac{x(ax^2 + bx + c)}{3x^2}
\]
Simplifying:
\[
L = \lim_{x \to 0} \frac{ax^2 + bx + c}{3x}
\]
Step 2: Evaluate the limit
As \( x \to 0 \), the expression simplifies to:
\[
L = \frac{c}{0}
\]
Since \( c > 0 \), the limit does not exist, so the correct answer is (d) None of these.