The correct answer is D) across-the-line starters. Across-the-line starters are the most common starting equipment used for three-phase induction motors of five horsepower or less. This is because these smaller motors can be started directly from the full line voltage without the need for reduced voltage starting, which is required for larger motors to limit the high inrush currents and torque produced during startup. Across-the-line starters simply connect the motor directly to the three-phase power supply, allowing the motor to start at full voltage and speed. The other options, such as autotransformer, resistor, and reactor starters, are typically used for larger three-phase induction motors that require reduced voltage starting to protect the electrical system and the motor itself during startup.