The correct answer is C) autotransformer. An autotransformer is a type of electrical transformer that uses a single winding to step up or step down the voltage. In the illustration EL-0083, the device shown in figure "B" between the source circuit breaker and the load is an autotransformer, which is used to adjust the voltage level as needed for the load. The other answer choices are incorrect because a fluorescent light ballast (A) is used to regulate the current in a fluorescent light, a power factor correction inductor (B) is used to improve the power factor of the circuit, and a noise filtering choke (D) is used to reduce electrical noise or interference, rather than adjusting the voltage level.