An energy difference of 4×10-3 eV for the 3p subshell of sodium accounts for the how many splitting of a spectral line at 589.3 nm is（）

An energy difference of 4×10-3 eV for the 3p subshell of sodium accounts for the how many splitting of a spectral line at 589.3 nm is（）
A.1.2 nm
B.1.1 nm
C.1.8 nm
D.0.6 nm
正确答案：1.2 nm