Explanation:

Compound DC Generator:
- A compound DC generator is a type of electrical generator that is designed to provide a more stable output voltage by combining the features of both series and shunt-wound generators.
- In a compound DC generator, there are two sets of field windings - one is connected in series with the armature winding, and the other is connected in parallel (shunt) with the armature winding.

Types of Compound DC Generators:
- Compound DC generators can be classified into three main types based on the connection of the series and shunt field windings: over, under, and level compounded generators.
- Over compounded generators have a series field winding that produces a magnetic flux in the same direction as the shunt field winding, resulting in a higher output voltage than a level compounded generator.
- Under compounded generators have a series field winding that produces a magnetic flux in the opposite direction to the shunt field winding, resulting in a lower output voltage than a level compounded generator.
- Level compounded generators have a series field winding that produces a magnetic flux that is proportional to the armature current, resulting in a relatively constant output voltage across varying loads.

Commercial Compound DC Generators:
- Most commercial compound DC generators are typically supplied by manufacturers as over compounded machines.
- Over compounded generators are commonly used in applications where a relatively stable output voltage is required, such as in industrial settings or power plants.
Therefore, the correct answer to the question is option 'A' - over compounded.