DC Generators
To avoid formation of grooves in the commutator of a D.C. machine

All of these
The brushes of same polarity should track each other
Brush position has no effect on the commutator grooving
The brushes of opposite polarity should track each other

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DC Generators
Lap winding is composed of

That even number which is exact multiple of poles
That even number which is exact multiple of poles + 2
Any even number of conductors
Any odd number of conductors

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