Polychlorinated biphenyls (pcbs) that cause cancer and birth defects are classified as a. carcinogens b. contamination c. pollution d. toxigens

The correct answer is A.
Various substances, like in our example PCBs can promote the development of cancer cells. Cancer cells are cells that divide and proliferate at a greater rate than other cells, competing with them for nutrients. Carcinogens often cause DNA damage, that can lead to cancer cell development.