A Metastable State Is Important for the Generation of a Laser

Multiple Choice

A metastable state is important for the generation of a laser beam because it assures that:

A) spontaneous emission does not occur more often than stimulated emission
B) photons do not split too rapidly
C) more photons are emitted than are absorbed
D) photons do not collide with each other
E) photons do not make upward transitions