The correct option is C IgA
Different immunoglobulins are produced by specific immune cells called plasma cells, in response to stimulation by any foreign pathogenic antigen. IgA is the predominant secretory antibody that is found in our body. IgA are found in the blood, and also in saliva, tears, gastric secretions and breast milk etc. IgA provides protection against infection in mucosal areas such as respiratory and gastrointestinal tracks. Significant amounts of IgA are not produced in a baby until six months and hence they are supplemented by the mother through breast milk.
Other three antibodies given in options play specific roles in fighting the pathogen invading a body, but IgA specifically plays a role as a secretory antibody.