Final answer:
A perfectly black body A) absorbs all incident radiation and is defined as a blackbody, which ideally absorbs and then re-emits energy across all wavelengths. Real objects, like a black T-shirt, are not perfect blackbodies because they reflect some light.
Step-by-step explanation:
A perfectly black body is one that A) Absorbs all the incident radiation. This characteristic defines a blackbody, which is an idealized physical body that absorbs all electromagnetic radiation that falls onto it. In practical terms, no real object acts as a perfect blackbody because all materials reflect some portion of incident radiation. For instance, a black T-shirt may be a good approximation of a blackbody but it is not perfect because it reflects some light, making option a. the correct answer. In contrast to a black T-shirt, an ideal blackbody would also re-emit energy across all wavelengths of the electromagnetic spectrum. This property is crucial for astronomers when studying objects like stars, which despite emitting light, are considered blackbodies because they absorb all incident radiation and re-emit it.
Absorptive surfaces more closely model a perfect blackbody than reflective surfaces because they are better at absorbing radiation, which is consistent with the properties of a blackbody. Therefore, in the context of the question, absorptive surfaces are closer to being a perfect blackbody than reflective surfaces. In summary, blackbodies not only absorb electromagnetic radiation but also emit blackbody radiation, which is electromagnetic radiation emitted by a blackbody.