The importance of including citations and a works cited page within a research paper can be attributed primarily to:
A. To support an argument - Citations provide evidence for your claims, adding credibility and weight to your argument.
D. To avoid plagiarism - Proper citations give credit to the original authors of the works you reference, helping you avoid plagiarism and academic dishonesty.
While options B and C (to sound professional and to use correct formatting) are also relevant, the key reasons for including citations and a works cited page are primarily to support your argument and to avoid plagiarism. Therefore, A and D are the most important reasons.