DC Motors
Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control

All above can be used
Four point starter is used
Drum type controller is used
Three point starter is used

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DC Motors
In variable speed motor

Same commutating field is needed at low speed than at high speed
None of these
A stronger commutating field is needed at low speed than at high speed
A weaker commutating field is needed at low speed than at high speed

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