The correct answer is D) disconnecting coil ends, insulating each, and short circuiting the two commutator bars. This is the correct answer because it is a temporary repair method that can allow continued operation of an open DC propulsion armature coil until permanent repairs can be made. By disconnecting the coil ends, insulating them, and short circuiting the two commutator bars, the open circuit in the coil is bypassed, allowing the motor to continue running without that faulty coil. The other options are incorrect because they would either ground the coil (A), remove essential components like the brushes (B), or directly connect the coil ends to the brushes (C), which would not properly address the open circuit issue and could lead to further damage.