Biology Help!

Edward Jenner is considered the founder of vaccines in the western world. In 1796, he inoculated a 13 year-old-boy with the virus that caused cowpox. Since cowpox and smallpox are closely related, the result was a demonstrated immunity to smallpox. Later, the first smallpox vaccine was developed. During the next two centuries, systematic implementation of mass smallpox immunizations culminated in its global eradication in 1979.
Using the cowpox virus to create a virus for smallpox ...

A) ...allowed only expectant mothers to pass the immunity on to their unborn children.
B) ... induced a secondary response because the body immediately recognized cowpox as smallpox due to the similarities in their genetic blueprints.
C) ...induced a primary immune response and immunological memory. Because of this, an encounter with the pathogen would trigger a rapid and strong secondary response.
D) ...allowed the virus to lie dormant within the cells of the person. When introduced to the virus again, the body could use the dormant pathogen as a point of reference.