Why can't your research report include just opinions? A. Opinions are not appropriate for school reports.
B. A research report containing only your opinions will not be long enough.
C. Opinions usually not convincing without reasons and evidence.
D. Most people are easily offended by other people's opinions.

C. Opinions usually are not convincing without reasons or evidence.

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 :)

a. inform

explanation:

"how to" tells us that it will explain how to, which means to inform