Environmental agents such as a drug, chemical, virus or other factor that produce a birth defect are known as teratogens. The correct option in regards to the given question is option "C". The mother of the child can be exposed during her pregnancy to something in the environment that can be the reason for defective birth of a child.Teratogen is an agent that has the power to disturb the growth of an embryo or fetus. This agent also has the power of creating a miscarriage or permanently stopping the process of pregnancy. Radiations can be another cause for teratogen.