Answer:
C. Opinions usually are not convincing without reasons or evidence.
Step-by-step explanation:
I don't really know the context to this question but I would assume the answer is C because research reports are very heavily focused on exactly what it's called; research. A research report is usually answering a question or proving your point to an argument so your opinion would be on which side you would be taking for example here is a research question: should schools allow phone usage in school?
Your opinion would be either yes or no but what makes it a research report is the amount of evidence you will use in your body paragraphs to support the side you are opinionated towards.
Hope this helped :)