Final answer:
Shivering and vasoconstriction act to maintain warmth in the body's keep the core organs warm option (d) by generating heat and reducing blood flow to the extremities, respectively, as a defense against cold exposure.
Step-by-step explanation:
Shivering and vasoconstriction are the body's defenses in order to keep the core organs warm option (d). These responses to cold are crucial for maintaining homeostasis. Shivering involves random muscle movement that generates heat, whereas vasoconstriction reduces blood circulation to the extremities, like the hands and feet, to prevent the cooling of blood and maintain warmth where it's most needed around the vital organs. This process is essential to protect the body's core temperature and thus prevent potential harmful effects such as confusion, lethargy, and severe cases, loss of consciousness, and death due to a significant drop in core temperature.
Frostbite is a risk when blood flow to areas like fingers and toes is greatly reduced; however, this is a different response intended to preserve core warmth rather than protect the appendages themselves. Hence, vasoconstriction and shivering work primarily to safeguard the internal organs by conserving heat.