instruction:
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.
question:
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.
answer:
When was the Polio vaccine created?


question:
No evidence has yet been found of a Jewish presence in antiquity in Germany beyond its Roman border, nor in Eastern Europe. In Gaul and Germany itself, with the possible exception of Trier and Cologne, the archeological evidence suggests at most a fleeting presence of very few Jews, primarily itinerant traders or artisans. A substantial Jewish population emerged in northern Gaul by the Middle Ages, but Jewish communities existed in 465 CE in Brittany, in 524 CE in Valence, and in 533 CE in Orleans. Throughout this period and into the early Middle Ages, some Jews assimilated into the dominant Greek and Latin cultures, mostly through conversion to Christianity.[better source needed] King Dagobert I of the Franks expelled the Jews from his Merovingian kingdom in 629. Jews in former Roman territories faced new challenges as harsher anti-Jewish Church rulings were enforced.
answer:
Who expelled the Jews from his Merovingian kingdom in 629?


question:
To put it another way, a thing or person is often seen as having a "defining essence" or a "core identity" that is unchanging, and describes what the thing or person really is. In this way of thinking, things and people are seen as fundamentally the same through time, with any changes being qualitative and secondary to their core identity (e.g. "Mark's hair has turned gray as he has gotten older, but he is still the same person"). But in Whitehead's cosmology, the only fundamentally existent things are discrete "occasions of experience" that overlap one another in time and space, and jointly make up the enduring person or thing. On the other hand, what ordinary thinking often regards as "the essence of a thing" or "the identity/core of a person" is an abstract generalization of what is regarded as that person or thing's most important or salient features across time. Identities do not define people, people define identities. Everything changes from moment to moment, and to think of anything as having an "enduring essence" misses the fact that "all things flow", though it is often a useful way of speaking.
answer:

What did Whitehead believe were essentially the only things that truly exist?