The correct answer is A) placing a magnetic compass near each field. To test for a reversed shunt field coil in a DC motor, you can connect the coil to a low voltage source and then use a magnetic compass to check the polarity of the field. If the field is reversed, the compass needle will indicate the opposite polarity when placed near the field coil. This method allows you to quickly identify any issues with the field coil wiring or connections. The other options are incorrect because: B) connecting a copper jumper across the interpole connections would not test the shunt field coil, C) placing an iron bar across each field would not provide a clear indication of polarity, and D) connecting a test lamp across adjacent fields would not specifically test for a reversed shunt field coil.