Which combination of gland and hormone would be linked to winter hibernation and spring reproduction in bears?

The correct option is A Pineal gland, melatonin
The pineal gland is buried deep in the brain and functions as an endocrine gland by secreting the hormone melatonin. In some vertebrates, melatonin helps to regulate reproductive physiology in species with distinct breeding seasons. Melatonin plays a very important role in the regulation of a 24-hour (diurnal) rhythm of our body and is also responsible for other rhythms like hibernation, fur color changes, and migration in animals.