This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

During the years 1940-1955, the rate of decline in the U.S. death rate accelerated from 2% per year to 8% per year, then returned to the historical rate of 2% per year. The dramatic decline in the immediate post-war years has been attributed to the rapid development of new treatments and vaccines for infectious disease that occurred during these years. Vaccine development continued to accelerate, with the most notable achievement of the period being Jonas Salk's 1954 development of the polio vaccine under the funding of the non-profit National Foundation for Infantile Paralysis. The vaccine process was never patented, but was instead given to pharmaceutical companies to manufacture as a low-cost generic. In 1960 Maurice Hilleman of Merck Sharp & Dohme identified the SV40 virus, which was later shown to cause tumors in many mammalian species. It was later determined that SV40 was present as a contaminant in polio vaccine lots that had been administered to 90% of the children in the United States. The contamination appears to have originated both in the original cell stock and in monkey tissue used for production. In 2004 the United States Cancer Institute announced that it had concluded that SV40 is not associated with cancer in people.
When was the Polio vaccine created?

Academic higher education in Estonia is divided into three levels: bachelor's, master's, and doctoral studies. In some specialties (basic medical studies, veterinary, pharmacy, dentistry, architect-engineer, and a classroom teacher programme) the bachelor's and master's levels are integrated into one unit. Estonian public universities have significantly more autonomy than applied higher education institutions. In addition to organising the academic life of the university, universities can create new curricula, establish admission terms and conditions, approve the budget, approve the development plan, elect the rector, and make restricted decisions in matters concerning assets. Estonia has a moderate number of public and private universities. The largest public universities are the University of Tartu, Tallinn University of Technology, Tallinn University, Estonian University of Life Sciences, Estonian Academy of Arts; the largest private university is Estonian Business School.
What are the three levels of higher learning in Estonia?

Until the 16th century, the Low Countries corresponding roughly to the present-day Netherlands, Belgium, and Luxembourg consisted of a number of duchies, counties, and Prince-bishoprics, almost all of which were under the supremacy of the Holy Roman Empire, with the exception of the county of Flanders, which was under the Kingdom of France.
The Low Countries were made up of which present day countries?