Answer:
D - his advice about training can be trusted.
Step-by-step explanation:
The details about Larry Greene's expertise as an exercise science expert, former professional distance runner, and coach suggest that he has a strong background in running and training. Therefore, his advice about preparing for a mile run can be trusted. The paragraph also mentions that he is a coauthor of a book about training for young distance runners, but this information is not the main focus of the paragraph.