ANS:B - does not remain constant

Fluctuation is something that you can observe in real-time quick and observable variation but declination variation is slow and small. So we don't select fluctuation. B) does not remain constant and C) Fluctuates, Both are the same meaning. So Both B&C are right answers. Magnetic declination occurs only when magnetic needle which is present in the compass comes under the influence of any magnetic material present nearby it. As it depends upon the magnetic property of the material that's why it can't remain constant. Image result for Magnetic declination.

Magnetic declination or variation is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the direction of the Earth's magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole).