The correct answer to this question is D, Power supply. The most common use of power supplies is associated with computers. There are three types of power supplies. The first is called unregulated. It is made up of a transformer, low-pass filter, and a rectifier.
Compared to other power supplies, they are lower cost and efficient. The second type is linear regulated. It outputs a fixed voltage for a wide range of inputs. The third type is switching. It combines elements of both the unregulated and direct supplies. This means it is cost-effective, efficient, while also small in size.