Final answer:
The best sentence to add between sentences A and B, to maintain the professional tone of Jane's letter to Dr. Anne Jones, is option (b), which highlights the national recognition of Plum College's ecology program.
Step-by-step explanation:
The student, Jane, is drafting a formal letter to Dr. Anne Jones and is looking to add a sentence that best complements the professional tone of her letter between sentence A and sentence B. Given the context and tone of the letter, the best option would be option (b): The school has an ecology program that has been recognized nationally. This sentence maintains the formality and focus on Jane's academic and professional interests in ecology, aligning with her intention to list Dr. Anne Jones, an environmental sciences expert, as a reference in her scholarship application to Plum College.