A Laser with Wavelength of 633 Nm Is Used to Excite

A laser with wavelength of 633 nm is used to excite a gas of atoms which strongly absorb radiation at 638 nm.Which gas atoms will absorb the laser radiation best?

A) An atom that is moving toward the laser at 2.4 * 10⁶ m/s.
B) An atom that is moving away from the laser at 2.4 * 10⁶ m/s.
C) An atom that is moving away from the laser at 1.2 * 10⁶ m/s.
D) An atom that is moving toward the laser at 1.2 * 10⁶ m/s.
E) An atom that is that is at rest with respect to the laser.