Answer:
D. history of The Star-Spangled Banner
Explanation:
We want a topic that <em>limits</em> the broad subject of music, which means we want something that is as specific as possible.
Look at the answer choices:
- A: famous pianists
Well, there are numerous famous pianists: Mozart, Beethoven, Chopin, Ray Charles, Stevie Wonder... The list goes on, so this is still a very broad topic. Eliminate A.
- B: modern rap music
There is so much to talk about with regards to modern rap music: the intonations, history, famous rappers, etc. Again, this is broad, so eliminate.
- C: history of the harmonica
This is a bit more narrow, as we've cut down to one specific instrument. However, there's still so much to talk about with regards to this history: origins, makers, evolution of the structure, etc. Eliminate C.
- D: history of The Star-Spangled Banner
Ah, now this is definitely very narrow because we've chosen a very specific song to focus on. Thus, D is the answer.