Brown adipose tissue is present in large amounts in the newborn, which helps offset the extensive heat loss, that results from the newborn's high surface-to-mass ratio and avoids lethal hypothermia. In newborns, brown adipose tissue makes up about 5% of the total body mass and is located on the back, along the upper half of the spine, and towards the shoulder. The amount gradually decreases as the body grows and is maximum at the 3rd month of the postnatal life. So, the correct answer is option B.