Correct Option: A

Adjuvants are compounds that enhance the specific immune response against co-inoculated antigens. Adjuvants can be used for various purposes: (i) to enhance the immunogenicity of highly purified or recombinant antigens; (ii) to reduce the amount of antigen or the number of immunizations needed for protective immunity; (iii) to improve the efficacy of vaccines in newborns, the elderly or immuno-compromised persons; or (iv) as antigen delivery systems for the uptake of antigens by the mucosa. Some of the features involved in adjuvant selection are: the antigen, the species to be vaccinated, the route of administration and the likelihood of side-effects.