The passage details Dr. Alvarez's roles in reverse chronological order. It begins with her current role as executive director, (D), and then discusses her previous position as a lab director, (C), at J.G. Laboratories. The transitional phrase "prior to" in the next sentence indicates that she was an adjunct professor, (B), before she became a lab director. No earlier roles are mentioned for Dr. Alvarez, though choice (D) may have been tempting because one is generally a graduate student before becoming a professor. However, the question asks for the earliest role mentioned in the announcement and is not asking you to infer what other roles Dr. Alvarez may have held.