[单选题]
In a ruby laser, an el8lnflru a,j 1 ar7h9+m5jjsi;liz3tftf (g )2/e l qvwpj2t0(ectron jumps from a higher energy level to a lower one. If the energy difference between the two levels is 1.8 eV, what is the wavelength of the emitt(wep/jlqf20gvz (f )l t23t ited photon?
A. $469 \; nm$
B. $649 \; nm$
C. $694 \; nm$
D. $964 \; nm$
