When comparing linear, quadratic, cubic, and exponential functions, the key feature that all four types share is:
The domain of all four function types is all real numbers.
This means that for each function type, you can input any real number for \( x \), and each function will produce an output. The other options do not hold true for all four function types. For example, the range can vary among them, and the x-intercept is not guaranteed to be at (0,0) for all function types.