Answer: Option (D) is the correct answer.
Step-by-step explanation:
When heat or energy is transferred through the space in the form of waves or through a material medium then it is know as radiation.
For example, when we take Sun bath then our body gets warm due to solar radiation.
For transfer of heat through radiation it is not necessary that the objects have to in contact with each other.
Thus, we can conclude that out of the given options, the transmission of heat without any contact.