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.

Q: Between 2000 and 2004 an average of 478 crimes were reported each day in Mexico City; however, the actual crime rate is thought to be much higher "since most people are reluctant to report crime". Under policies enacted by Mayor Marcelo Ebrard between 2009 and 2011, Mexico City underwent a major security upgrade with violent and petty crime rates both falling significantly despite the rise in violent crime in other parts of the country. Some of the policies enacted included the installation of 11,000 security cameras around the city and a very large expansion of the police force. Mexico City has one of the world's highest police officer-to-resident ratios, with one uniformed officer per 100 citizens.

A: How many crimes occurred around the turn of the latest century? 
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Q: Following the end of World War II the educational gap between White and Black Americans was widened by Dwight D. Eisenhower's GI Bill. This piece of legislation paved the way for white GIs to attend college. Despite their veteran status returning black servicemen were not afforded loans at the same rate as whites. Furthermore, at the time of its introduction, segregation was still the law of the land barring blacks from the best institutions. Overall, "Nearly 8 million servicemen and servicewomen were educated under the provisions of the GI Bill after World War II. But for blacks, higher educational opportunities were so few that the promise of the GI Bill went largely unfulfilled."

A: What major event preceded the growth of the divide in education between White and Black Americans?
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Q: Hydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxiant in its pure, oxygen-free form. In addition, liquid hydrogen is a cryogen and presents dangers (such as frostbite) associated with very cold liquids. Hydrogen dissolves in many metals, and, in addition to leaking out, may have adverse effects on them, such as hydrogen embrittlement, leading to cracks and explosions. Hydrogen gas leaking into external air may spontaneously ignite. Moreover, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns.

A:
What threats can hydrogen cause to human saftey?
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