Explanation: A switching electronic voltage regulator operates by rapidly turning a control device, typically a transistor, fully on or fully off. It doesn't continuously vary the resistance like a linear regulator. The proportion of time the device is "on" versus "off" within each switching cycle is called the duty cycle. **C) Switches the control device on or off, with the duty cycle proportional to the line or load conditions.** This is the core principle of a switching regulator. By adjusting this duty cycle, the regulator controls the average voltage delivered to its output filter, thereby maintaining a stable output voltage despite changes in the input (line) voltage or the current drawn by the load. This method is highly efficient because the control device dissipates very little power when fully on or fully off. **A) Varies the conduction of a control element in direct proportion to the line voltage or load current.** This describes a *linear* voltage regulator, which operates its control element in its active region, effectively acting as a variable resistor to drop excess voltage. Linear regulators are less efficient than switching regulators because they dissipate more power as heat. **B) Provides more than one output voltage.** While some power supplies may offer multiple outputs, this is a feature of a specific design, not the fundamental operating principle of *all* switching regulators. Many provide only a single output. **D) Gives a ramp voltage at its output.** The purpose of any voltage regulator is to provide a *stable DC output voltage*, not a varying ramp voltage. The internal control circuitry might use ramp generators, but the final output is smoothed into a constant DC level.