Vaccines have been around since 1796 preventing people from diseases and decreasing death rates. I believe due to the modern vaccines and medicine people have been living longer than life expectancies in the 1700's and 1800’s, which was between 30 and 40 years. Vaccines train the human body to recognize viruses or bacteria and the antigens (molecule capable of inducing an immune response) will start attacking the virus or bacteria before it tries to spread and cause sickness once it is has recognized it. However, vaccines are not always 100% safe because they can come with side effects. For example, the Hepatitis B vaccine had a severe allergic reaction, called anaphylaxis which caused difficulty breathing, dizziness, and skin rashes for a few people.
Pretty confident that it is A, judging by that the word composition is used as a combination or a ratio of 2 things. Also none of the other options make sense.
