The correct answer is D) disconnecting coil ends, insulating each, and short circuiting the two commutator bars. This is the correct answer because it allows the armature coil to be temporarily bypassed while preventing a short circuit that could damage the DC propulsion system. Disconnecting and insulating the coil ends isolates the damaged coil, while short-circuiting the commutator bars allows the armature to continue rotating without the faulty coil. This provides a temporary solution until permanent repairs can be made. The other options are incorrect because A) directly connecting the coil ends to brushes would create a short circuit, B) removing the brushes would prevent the armature from rotating, and C) grounding the coil ends and shorting the commutator bar would also create a short circuit, potentially damaging the system.