I don't know fully so I'll narrow it down to two answers.
B and D, I'm sorry for not giving the correct answer
Answer:
I believe it is answer C.
Explanation:
Reason being is because the Talented Tenth is a term designated for a leadership class of African Americans in the 20th century.
The correct answer is Mendelssohn would send his letters to his sister Fanny whom was also a musical prodigy.