To avoid plagiarism when including a direct quotation in a research paper, the key step is:
The source must be properly cited.
Proper citation ensures that the original author is credited for their work, thereby preventing any form of plagiarism. While including a direct quote, you should also maintain the integrity of the quotation and follow the specific citation style required for your paper (e.g., APA, MLA, Chicago, etc.).
The other options listed do not directly address the issue of plagiarism related to direct quotations. Rephrasing is more relevant to paraphrasing than quoting directly, and while bias should be considered in research, it is not specifically related to plagiarism. Additionally, the source being about the same topic is not a requirement for avoiding plagiarism.