Answer: A. Reference a specific project the person has worked on recently to show you did a deep dive into his/her background.
Step-by-step explanation:
If you were to write an application letter for employment at a company, you would include certain details of the company that you found out whilst researching them so that your chances of being hired are improved.
The logic is the same here. In order to prove that you have researched a person, the proof lies in what you found out during that research. In this scenario, that includes specific projects that the person has worked on of recent.