Correct option is D
Brushes are usually made from carbon or graphite.
They rest on commutator segments and slide on the segments
When the commutator rotates keeping the physical contact to collect or supply the current.
Brushes are made up of Carbon and graphite to reduce the wear and tear of the commutator.
When a brush is at any particular segment, it shorts out that particular coil and draws current from the rest of the coils
The carbon brush makes sure the commutation process remains free from sparks
Helps to conduct electric current between the moving parts of the motor.
The voltage drop across the brush contact is around 2 volts.
