None of the above. The problem this addresses is facing each front wheel the correct direction when turning. Imagine fixing a pair of bicycles together at the

None of the above. The problem this addresses is facing each front wheel the correct direction when turning. Imagine fixing a pair of bicycles together at the bodies. When you want to go around a corner, the inner bicycle will have to turn more sharply than the outer one (which in turn has to go faster). That means that the front wheel needs a higher angle of deflection on the inside than the outside. The same dynamic exists in a true 4-wheel vehicle, except that there is a mechanical linkage that allows you to steer both front wheels together instead of independently. The problem this linkage geometry solves is the problem of getting the inner wheel to deflect further than the outer wheel, by approximately the right amount. (iirc, this geometry doesn't get that perfect, and modern cars use a variant that's a bit more accurate. But that's a small optimization compared to the improvement this provides over just making the wheels both turn the same angle.) The problem a differential solves is allowing the wheels on the outside edge to spin faster even when sharing an axle with the wheels on the inside edge.