!Please help fast!!*18 pts*!

How is light amplified in a laser?
A. Photons "leak" through a partically reflecting mirror, causing them to travel in step.
B. Integrated circuits in a laser amplify the sound produced by photon emission.
C. Photons collide with gas particles, multiply, and reflect back and forth in a tube.
D. Electric current is amplified and directed into gas particles, which emit photons.