Flat earthers are going to chose the third answer.
If one of you lives near the equator (measures say that g = 9.78 there) and another around 45° north or south (g = 9.81), two simple chronophotographies could determine if g varies with the latitude. Looks like the experiment could easily be made, and will definitely prove if the third answer could or could not be true.
EXPERIMENTDefinitions : "gravitationnal acceleration" means here the acceleration of the objects towards Earth, either by gravity (round earth theory) or by Earth's acceleration (flat earth theory)
Question : Does gravitational acceleration varies with the latitude ?
Implications : If gravitationnal acceleration effectively varies, the third answer could not be possible, and the modern scientifical measures are confirmed. If it does not, the earth could not be an oblate spheroid as the scientists think it is.
Hypothesis : The scientifical-admitted theory is that, the Earth being an oblate spheroid, gravitationnal acceleration effectively varies.
Experiment : Two persons, one around 45° and one near the equator, will drop regular ping-pong balls from the height of 1.5 meters, and will make a chronophotography.
Data analysis : If the photographical evidence shows a visible difference between the two tests, and we could calculate from this gravitationnal constants compatible with the modern scientific data, we could consider the answer is "Yes". If there is no visible difference between the two chronophotographies, and precision is high enough to determinate there is no difference at a scale of 0.02 m/sē, the answer will be "No".