Choose the correct statement below:
A. A pathogen is an infectious disease causing agent and all pathogens are viruses.
B. A bacterium is an infectious disease causing antigen and all pathogens are bacteria.
C. An antigen is an infectious disease causing agent and all antigens are organisms.
D. A pathogen is an infectious disease causing agent and some pathogens are nonliving viruses.
E. A pathogen is an infectious disease causing bacterium and all pathogens are organisms.
F. An antigen is an infectious disease causing virus and some antigens are bacteria.