What motion causes earth to take the shape of an oblate spheroid instead of that of a true sphere?

The correct answer to this open question is the following.

Although there are no options attached, we can say the following.

The motion that causes the earth to take the shape of an oblate spheroid instead of that of a true sphere is the oblate ellipsoid, which is the result of rotating an ellipse in its shorter axis.

Yes, scientists have confirmer that although in many beautiful protographs planet Erath seems to be a perfect sphere, it is not. Its shape is flattened at the North and South pole. The named scientists use is of an "oblate spheroid."

the answer is a) to be able to obey them.