The Earth is not a perfect sphere but is slightly flattened at the poles and bulging at the equator due to its rotation. This shape is often referred to as an oblate spheroid, meaning it is mostly spherical but slightly flattened at the poles and slightly bulging at the equator. The flattening is a result of the Earth's rotation, which causes it to be slightly compressed along its axis.

The sea that does not belong to Russia is (B) Baltic Sea. The Baltic Sea is located in Northern Europe and is bordered by several countries, including Sweden, Finland, Denmark, Germany, Poland, Latvia, Estonia, Lithuania, and Russia. It is not entirely enclosed by Russia. The other seas mentioned (Laptev Sea, Kara Sea, and White Sea) are all located in the Arctic and subarctic regions and are part of the Russian territory.