Which of the following methods is safe to use when warming a person who has hypothermia?

Applying warm water bottles to the person's torso is a safe method for warming someone who has hypothermia. This approach helps to gradually raise the person's body temperature without the risk of causing additional harm. By placing the warm water bottles on the torso, the heat can be effectively transferred to the core of the body, which is critical in treating hypothermia.

Gradual warming is key to avoid shock or further complications, which can occur with methods that heat the body too quickly or apply heat directly to the skin. For example, using a heating pad directly on the skin can lead to burns or damage, while submerging someone in hot water can also cause shock to the body due to the sudden temperature change. Wrapping a person in cold towels is counterproductive, as it would further lower their body temperature and aggravate the hypothermia. Thus, using warm water bottles strikes a balance between providing warmth and ensuring safety during the re-warming process.