What type of signal uses continuous variations of a physical characteristic over time to transmit information?

The correct choice is an analog signal because it is defined by continuous variations in its physical characteristics, such as voltage, current, or electromagnetic waves, which can change smoothly over time. This allows analog signals to represent information in a format that mirrors real-world phenomena, enabling them to accurately convey changing conditions.

In contrast, a digital signal represents data as discrete values or steps, involving binary states (typically 0s and 1s) rather than smooth transitions. Discontinuous signals suggest abrupt changes rather than continuous ones, which does not align with the fundamental nature of analog signals. Electromagnetic interference (EMI) signals refer to unwanted disturbances in electronic systems rather than a method of transmitting information. Therefore, the characteristics of analog signals encompass the essence of smooth, continuous information transmission.