Final answer:
The best concluding sentence for the paragraph about FDR's challenges and leadership during the Great Depression is the one that links his personal grit and tenacity to his ability to lead the nation effectively.
Step-by-step explanation:
From the provided context, the best sentence to conclude Tanya’s paragraph about Franklin Delano Roosevelt (FDR) is: B. Roosevelt's grit and tenacity in dealing with personal challenges undoubtedly assisted him in leading the nation through a harrowing and uncertain time. This sentence aptly summarizes Roosevelt's personal battles with polio and links his individual perseverance to his ability to lead the nation. It reflects on his strength of character which played a crucial role in his presidency, especially as he guided the United States through the Great Depression and undertook the New Deal. It encapsulates not only FDR's personal struggles but also his professional triumphs, making it the most cohesive conclusion to the given paragraph.