Who is at particular risk for hypothermia?

Answer: D — All of the above

Individuals who are particularly vulnerable to hypothermia include infants, those who are very lean, and individuals with Alzheimer's disease, making the choice of "all of the above" the most accurate answer. Infants have a higher surface area to volume ratio, which means they lose body heat more quickly than adults. Their ability to regulate body temperature is also not fully developed, making them susceptible to cold environments. People who are very lean may lack adequate body fat, which serves as an insulator against cold conditions. This lack of insulation can lead to a rapid decrease in body temperature when exposed to cold environments. Individuals with Alzheimer's disease are at risk as well, primarily due to potential cognitive impairments that may prevent them from recognizing or reacting appropriately to cold environments. They might not dress adequately for the weather or may become disoriented, increasing their risk of exposure to cold. Combining all these factors, it becomes evident that multiple groups are at heightened risk for hypothermia, validating the choice of "all of the above" as the correct answer.