Choice A is the correct answer. Use exponent rules.

1. Power rule: $(e^x)^3 = e^{3x}$.
2. Product rule: $e^{3x} \cdot e^{2x} = e^{3x+2x} = e^{5x}$.

💡 Strategic Tip:$(a^m)^n = a^{mn}$ and $a^m \cdot a^n = a^{m+n}$.

Choice B is incorrect because this incorrectly multiplies exponents. Choice C is incorrect because exponent is $5x$, not $3x^2$. Choice D is incorrect because this mixes up the rules.