The correct options are
A It is the small level of radioactive radiation present in the environment
B It originates from both natural and artificial sources
C Diagnostic imaging applications like x-rays are CT - scan and gamma rays are sources of background radiations
D Naturally occurring radioactive elements like radon also contribute to background radiations.
Background radiations are ionising radiations present everywhere in the environment. Background radiations originate from a variety of sources, both natural and artificial. Sources include cosmic radiations, naturally occurring radioactive elements such as radon, and fallout from the testing of nuclear weapons and nuclear accidents. Medical imaging is also a major contributor to artificial background radiations.