Answer:
a. Stars all warm objects
c. Some unstable atomic nuclei
Step-by-step explanation:
Gamma rays are photons of very high energy (beyond 100keV) enough to remove an electron from its orbit.
They have a very short wavelength, less than 5 meters from the peak, and can be produced by nuclear decay, especially in the breasts of massive stars at the end of life.
They were discovered by the French chemist Paul Villard (1860 to 1934).
While X-rays are produced by electronic transitions in general caused by the collision of an electron with an atom at high speed, gamma rays are produced by nuclear transitions.
Gamma rays produce damage similar to those caused by X-rays or ultraviolet rays (burns, cancer and genetic mutations).
The sources of gamma rays that we observe in the universe come from massive stars (hypernovas) or some warm objects on the space that end their lives by a gravitational collapse that leads to the formation of a neutron star or a black hole, as well as unstable radioactive nuclei that emit radiation gamma to reach its steady state.