An electrical device which prevents an action from occurring until all other required conditions are met is called a/an （）.

A.relative speed of the rotor poles
B.number of turns of wire in the armature coil
C.strength of the magnets used
D.output voltage

A.loss of residual magnetism
B.absorption of moisture in the insulation
C.insulation varnish flaking
D.dirt collecting on the windings

A.inductance
B.capacitance
C.resistance
D.amperage