Travis is writing an essay over the advancement of the polio vaccine in the 1950s. Before the vaccine, people were vulnerable to a disease that could cause paralysis. The development of the vaccine helped save many lives.

Which of the following would be the best source for Travis to use for his paper?

A.
a recent issue of a scientific magazine
B.
a map of diseases around the world
C.
an autobiography of the scientist who developed the polio vaccine
D.
a paper written by a person who survived the disease in the 1950s