Answer: Supporting details
Explanation:
The main feature of an informative text is to inform clearly and objectively. It presents citations, sources, data and research to prove its credibility. So we can understand that the supporting details is the correct answer.
Signal words are not the fundamental basis for informative text, because the vocabulary used should only be clear and objective.
As for structure, in the case of informative texts, structure, content overlaps with form.
In relation to diction, it has no connection to the structure of the text, because diction is to speech while we are talking about written and unspoken text.