The answer is A.
Radiation is a type of heat transfer that transfer heat by electromagnetic waves. Outside the visual color range, we cannot see it. But sure almost everything is emitting and absorbing radiation right now. This type of heat transfer works in almost every environment, including vacuum.
Radiation does not require physical contact, unlike conduction. That's why we can feel the heat of sun even it's not touching the earth.
Radiation also does not need the circulate of fluids, unlike convection. That's also why radiation works in vacuum state without any air or fluid.
Radiation is emitted by almost everything. But also absorbing radiation at the same time. So this rule doesn't apply to D. Even your shirt is emitting radiation, your bag is too!
