The correct answer is: C. high capacity transformers
Disc windings are a type of winding used in transformers. They are made up of a series of discs that are stacked together and then insulated. The discs are then connected to each other by a series of wires. Disc windings are used in high capacity transformers because they are more efficient than other types of windings. They are also less likely to overheat.
A. Short capacity transformers are typically used in low-power applications. They are not as efficient as disc windings and are more likely to overheat.
B. Medium capacity transformers are typically used in applications that require a moderate amount of power. They are more efficient than short capacity transformers, but not as efficient as disc windings.
D. Any of the above is not the correct answer because disc windings are not primarily used in short capacity transformers or medium capacity transformers. They are primarily used in high capacity transformers.