I would go with C, it sounds like the better option to me.
Hello, the correct answer would be D. When you are quoting something, of course, that sentence needs to be separated by quotation marks, and the comma needs to be inside the quote, so first comma, then close the quote. After that continue with the narration, put a comma, open quotation mark, write your quote, put a full stop, and close the quotation mark.
In a way, all of the options are correct: but most of them are not very explicit and too general. For example, a formal scientific study will as a result provide some insight into the topic: but this is not the direct goal of the study.
The best answer is that formal, scientific studies have the aim of testing the hypothesis- this is the correct answer.
