In a Gamma Camera, How Does the Energy Filter-Called the Pulse

In a gamma camera, how does the energy filter-called the pulse height analyzer-enhance image quality?

A) It uses several cameras around the source to get a 3-D image.
B) It shows all the energies of radiation by intensities, so that we can select only the specific gamma energy released by the isotope.
C) Only the specific gamma radiation released by the isotope is allowed to pass, eliminating all other gamma radiation, such as cosmic rays and radiation of terrestrial origin.
D) It allows only gamma radiation to pass, and later we select the specific energy released by the isotope.