To evade formation of grooves in the commutator of a machine, what should be done

To evade formation of grooves in the commutator of a machine, what should be done

1. Brush position has no effect on the commutator grooving
2. The brushes of opposite polarity should track each other
3. The brushes of same polarity should track each other
4. All of above

Correct answer: 2. The brushes of opposite polarity should track each other

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