I. The earth is not spherical but elliptical in shape II. Variation in latitude and longitude III. Rotation of the earth on its axis IV. Variation in the de...

I. The earth is not spherical but elliptical in shape

II. Variation in latitude and longitude

III. Rotation of the earth on its axis

IV. Variation in the density of the earthOn which combination of the above does the weight of an object vary on the earth's surface?