Choice A is the correct answer. Analyze properties of exponential functions.

1. Domain: You can raise $b$ to any real power, so domain is all real numbers ✓
2. Range: For $a > 0$ and $b > 0$, output is always positive (no x-intercept).
3. Shape: Exponential functions curve, not straight.

💡 Strategic Tip: Standard exponential $y = ab^x$ (with $a, b > 0$) never touches the x-axis.

Choice B is incorrect because$ab^x > 0$ for all $x$ when $a, b > 0$. Choice C is incorrect because the graph approaches but never reaches $y = 0$. Choice D is incorrect because exponential functions are not linear.