In many cases, when you catch an infectious disease, your blood produces antibodies against the infective organism. These antibodies remain in the blood or can be rapidly made so that you are immune to further attacks of the disease. You can acquire immunity by receiving injections of a harmless form of the pathogen or its inactivated toxin. The injected substance is called a vaccine. Pertussis, also known as whooping cough, is an extremely contagious disease caused by the Bordetella pertussis bacterium. The vaccine preparation uses the killed bacteria. The vaccine for diphtheria is produced from purified inactivated toxin from a strain of Corynebacterium diphtheriae. Polio is caused by the polio virus, a highly contagious virus specific to humans. Attenuation takes an infectious agent and alters it so that it becomes harmless or less virulent. So, the correct answer is 'A- 4, B- 3, C- 2, D- 1'