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.
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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: As soon as the Greek War of Independence broke out in 1821, several Greek Cypriots left for Greece to join the Greek forces. In response, the Ottoman governor of Cyprus arrested and executed 486 prominent Greek Cypriots, including the Archbishop of Cyprus, Kyprianos and four other bishops. In 1828, modern Greece's first president Ioannis Kapodistrias called for union of Cyprus with Greece, and numerous minor uprisings took place. Reaction to Ottoman misrule led to uprisings by both Greek and Turkish Cypriots, although none were successful. After centuries of neglect by the Turks, the unrelenting poverty of most of the people, and the ever-present tax collectors fuelled Greek nationalism, and by the 20th century idea of enosis, or union, with newly independent Greece was firmly rooted among Greek Cypriots.

Answer: What year did the Greek war of independence break out?

Question: Yale seniors at graduation smash clay pipes underfoot to symbolize passage from their "bright college years," though in recent history the pipes have been replaced with "bubble pipes". ("Bright College Years," the University's alma mater, was penned in 1881 by Henry Durand, Class of 1881, to the tune of Die Wacht am Rhein.) Yale's student tour guides tell visitors that students consider it good luck to rub the toe of the statue of Theodore Dwight Woolsey on Old Campus. Actual students rarely do so. In the second half of the 20th century Bladderball, a campus-wide game played with a large inflatable ball, became a popular tradition but was banned by administration due to safety concerns. In spite of administration opposition, students revived the game in 2009, 2011, and 2014, but its future remains uncertain.

Answer:
What do seniors crush to celebrate graduation?