What advantage does giving birth in the harshest part of winter give the grey seal pup

Grey seals breed in habitats where disturbance is kept to a minimal like a rocky shore, ice flows, and islands. They feed on cold open waters. When pups are given birth in early winter or late autumn, their skins are white with a yellowish tint. They are relatively helpless and rely on their mother's milk for the first few weeks after birth. They deposit a thick layer of blubber that will protect and allow them to adapt to the cold to sustain them when they will hunt for themselves. 

Ithink the answer is d.