Occurs when an energy source transfers heat directly to another subject space; an example would be an object becoming warm by sitting in the sunshine

The question is fishing for the answer "radiation", but it never manages to make itself completely unambiguous.

It doesn't make it clear that there is no material in the "subject space". It just tries hard to imply that with the example of sunshine.

If there's any material stuff on the way from the "source" to the "subject space", then conduction could also be an acceptable answer.