Certainly! The correct choice is: A. His explanation of the grammar lesson was clear from the outset. In this context, "explanation of" is the more appropriate because it is generally preferred when discussing a specific subject or topic. It indicates a more direct and focused connection between the explanation and the subject being explained. "Explanation about" can sound a bit more informal and might be used when discussing a broader or less specific topic. Good job on asking, and feel free to reach out if you have more questions!