The correct answers indicating warning signs that a person is close to experiencing frostbite are:
a) Hardened skin
b) Waxy skin that is colder than the area around it
c) Skin that looks paler than the area around it
Among these options, a) and b) are particularly associated with frostbite. Option d) (Shiny, rosy skin) is not typically associated with frostbite; rather, it might indicate a different condition, such as overheating or superficial skin damage.