C

Step 1: The absorption spectrum of sodium (Na) typically displays distinct lines corresponding to the transitions of electrons between energy levels. One of the most prominent lines in the spectrum is due to the transition from the 3p to the 3s energy levels.
Step 2: The main absorption line of sodium is centered around 589.0 nm, which consists of two closely spaced lines (D1 and D2), approximately at 589.0 nm and 589.6 nm.
Step 3: Therefore, both 589 nm and 589.6 nm are present in the absorption spectrum of sodium.
Conclusion: The correct answer is both options A and B are correct. Thus, the final answer is C.