[单选题]
In a ruby laser, an electron jumps from aqz9dsog; 9(j q8z8 sus dfiun7(1r6wqo 3, equ higher energy level to a lower one. If the energy difference between the two leveu13(oe f,qu ridnq7w6 ls is 1.8 eV, what is the wavelength of the emitted photon?
A. $469 \; nm$
B. $649 \; nm$
C. $694 \; nm$
D. $964 \; nm$
