The correct answer is A) the declination of the Moon. The diurnal inequality of the tides is caused by the declination of the Moon relative to the Earth's equator. When the Moon is at its maximum declination, either north or south, the difference in the heights of successive high and low tides is greatest, resulting in the diurnal inequality. This is because the Moon's gravitational pull is strongest when it is directly overhead or underfoot, creating unequal tidal ranges. The other options are incorrect because the Moon's perigee or apogee position (B and D) and changing weather conditions (C) do not directly cause the diurnal inequality of the tides, which is primarily driven by the Moon's declination.