Sorry - I might be missing something here - but isn't the answer wrong ...

The answer says - "There are 60 Nautical miles per degree of latitude, or one per minute of latitude. The length of a degree of Longitude varies from 60 nautical miles at the equator, to zero at the poles, so answer D would only hold true at the equator, not anywhere on earth. The answer is 'approximate' because the earth is an ellipsoid and not a perfect sphere, so there is some small variance in the length. "

Isn't it the degrees of latitude that get smaller approaching the poles? Hence - the answer would only be correct at the equator (ignoring the slight flattening around the poles..)

A definition of Nautical mile is - "A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet). ".

Meridians (i.e. lines of longitude) are great circles, but the equator is the only line of latitude that is a great circle.

Have I completely misread/misunderstood the question?