According to the information in "edward jenner and the history of smallpox and vaccination," which event occurred first in the historical timeline of smallpox?
a. the word variola became a common name for the disease.
b. herbs and cold treatments were used as remedies for the disease.
c. the phrase small pockes was used to distinguish the disease.
d. smallpox survivors were recognized to form immunity to the disease.

The correct answer is d smallpox survivors were recognized to form immunity to the disease.

Explanation:

Edward jenner invented the vaccination for small pox virus.The people who suffered from pox disease develops immunity to small pox virus by the mechanism of immunologic memory of adaptive immunity after getting cured from that pox disease .

        The development of immunologic memory against pox disease inside the body of smallpox survivors will boost the immune system during the further entry of the same virus(small pox virus).

    As a result the stimulated immune system will secrete antibodies and immunity regulatory proteins to cope up with that virus.

substitution is the answer in this case

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.