Batteries always use direct current. That eliminates A and C. The other part of the answers is just asking what direct/alternating means. Alternating currents change directions moving one way then another. Direct current only moves in one direction. Therefore, the answer is D, since the current is direct and direct currents move in one direction.
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We are asked in what manner can one make the motor run in reverse. One way to do so is to flip the magnet on the other side so that the opposite charge faces to the motor. The magnetic field induced by the magnet to the motor results to a reactive force opposite to the induced motion.
The strength of a field force changes with distance from the sourceof the field-stronger closer to the source, weaker farther away from the source. The source can be either a mass, a charged particle, or a magnetic pole.
