Step 1: Understanding the Concept
The beat frequency equals the difference of the two frequencies sounded together.
Step 2: Use A and C
\(n_1-n_3=1.04n_2-0.99n_2=0.05n_2=5\), so \(n_2=100\text{ Hz}\).
Step 3: Other frequencies
\(n_1=1.04\times100=104\text{ Hz}\) and \(n_3=0.99\times100=99\text{ Hz}\).
Step 4: Check
\(104-99=5\) beats per second, as given.
Final Answer:
The frequencies of A, B and C are 104 Hz, 100 Hz and 99 Hz.
\[ \boxed{\text{(D) }\text{104 Hz, 100 Hz, 99 Hz}} \]