The choices can be found elsewhere and as follows:
It changes color as it absorbs visible light from the radar set.
It softens and melts as it absorbs microwaves from the radar set.
It becomes radioactive after it absorbs gamma rays from the radar set.
It begins to fluoresce after it absorbs ultraviolet light from the radar set.
I think the correct answer from the choices listed above is the second option. The chocolate bar softens and melts as it absorbs microwaves from the radar set. Hope this answers the question.
