Select from the following list the etiology of ulcerative colitis. a. Inflammatory processes associated with microbial agents (e. g., measles, viruses, protozoans, mycobacteria) play a key role in UC pathogenesis.
b. The measles virus, as well as protozoans and myobacteria, have been linked as definitive causes of UC.
c. Depression and stress are known direct causative factors and have a strong correlation with periodic flares.
d. Smoking is a substantial risk factor for UC.
e. Genetic factors predispose to UC; however, the specific gene products have not yet been identified.