The correct answer is D. Self-excited generator.
A self-excited generator is a type of DC generator that uses its own output current to excite the field coils. This means that the generator does not need any external power source to start generating electricity.
The other options are incorrect because they do not have the ability to build up without any residual magnetism in the poles.
A series generator is a type of DC generator in which the field winding is connected in series with the armature winding. This means that the current flowing through the field winding is the same as the current flowing through the armature winding.
A shunt generator is a type of DC generator in which the field winding is connected in parallel with the armature winding. This means that the current flowing through the field winding is independent of the current flowing through the armature winding.
A compound generator is a type of DC generator that has both a series field winding and a shunt field winding. The series field winding is connected in series with the armature winding, while the shunt field winding is connected in parallel with the armature winding.
Residual magnetism is the magnetism that remains in a ferromagnetic material after it has been magnetized. This magnetism can be used to start the process of generating electricity in a DC generator.