Which of the following best describes the process of fluorescence?
a. Molecules emit a photon at lower energy when excited electrons return to the ground state.
b. Atoms emit a photon when the electrons are excited.
c. Molecules emit a photon when the electrons are excited.
d. Molecules emit a photon at the same energy when excited electrons return to the ground state.
e. Molecules emit a photon at higher energy when excited electrons return to the ground state.