Choice A is the correct answer. Check ratios and differences.

1. $f(x)$: Ratios $\frac{20}{10}=2$, $\frac{40}{20}=2$ → Exponential (base 2).
2. $g(x)$: Differences $15-10=5$, $20-15=5$ → Linear (slope 5).
3. Conclusion: $f(x)$ is exponential, $g(x)$ is linear.

💡 Strategic Tip: Constant ratios = exponential. Constant differences = linear.

Choice B is incorrect because it reverses the classifications. Choice C is incorrect because$g(x)$ has constant differences. Choice D is incorrect because$f(x)$ has constant ratios.