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Let's create an imaginary experiment and reduce the Earth to the size of a billiard ball. In this case, it turns out that the surface of the Earth, with all its high mountains and deep trenches, will be smoother than a billiard ball! But even in this case, the Earth will not be able to roll as smoothly as a billiard ball rolls on a cloth. This is because of the shape of the Earth. Our planet is not a perfect ball.

Determine the reason why the Earth was named "geoid".

• The Earth has a bulge at the equator.
• The Earth is flattened at the equator.
• The Earth has a bulge at the poles.
• The Earth is flattened at the poles.