Question

jonas salk and polio
polio is a viral disease that produces flu - like symptoms and may occasionally cause muscle weakness or paralysis. throughout the first half of the twentieth century, the disease was common, and parents feared that their children would lose the ability to move their arms or legs. in 1947, dr. jonas salk began studying polio at the university of pittsburgh in search of an answer. he discovered three basic types of polio viruses and began to develop a vaccine that would protect against all three. testing began in 1952, with vaccinations eventually given to about two million children. the vaccine was shown to be effective and was put into general use in 1955. jonas salk became a hero and received an award from president dwight d. eisenhower.
what is the main, or central, idea of the passage?
jonas salks vaccine for polio was tested in the early 1950s and put into general use in 1955.
jonas salk discovered that there were three different viruses that caused the disease called polio.
jonas salk developed a vaccine that provided protection against the feared disease polio.

Explanation:

The passage begins by introducing polio as a feared disease. Then it details Dr. Jonas Salk's work: starting to study polio in 1947, discovering three types of polio viruses, developing a vaccine, testing it (starting in 1952 with about two - million children vaccinated), and the vaccine being put into general use in 1955. The first two options are just details (testing and discovery of virus types) within the broader story of Salk developing the polio vaccine. The main idea encompasses the whole process of Salk's efforts leading to the development of a polio - protecting vaccine.

Answer:

Jonas Salk developed a vaccine that provided protection against the feared disease polio.