The correct answer is A. A labeled diagram of a car engine
Step-by-step explanation:
In a presentation elements such as photographs, videos, diagrams or audio should be selected depending on the purpose of the presentation, because the main objective of including them is to help the audience to understand your ideas as a speaker.
In this way, in the case of a mechanic giving a presentation about how to rebuild a car engine the best and most helpful element is "a labeled diagram of a car engine" because this visual element allows the audience to understand the different parts of the engine in terms of color, shape, and features, and this would help them to understand better how to rebuild a car engine by remembering the location and characteristics of each part. Also, this would facilitate the role of the speaker because he does not need to explain how each part looks like.