Antigens are foreign proteins that invade the systems of organisms. Vaccines function by stimulating an organism's immune system to develop antibodies against a particular antigen. Developing a vaccine involves producing an antigen that can be introduced into the organism being vaccinated and which will trigger an immune response without causing the disease associated with the antigen. Certain strains of bacteria can be used to produce antigens used in vaccines. Which of the following best explains how bacteria can be genetically engineered to produce a desired antigen? A. The gene coding for the antigen can be inserted into plasmids that can be used to transform the bacteria. B. The bacteria need to be exposed to the antigen so they can produce the antibodies. C. The DNA of the antigen has to be transcribed in order for the mRNA produced to be inserted into the bacteria. D. The mRNA of the antigen has to be translated in order for the protein to be inserted into the bacteria.