Here is a question about this article: The first hydrogen-filled balloon was invented by Jacques Charles in 1783. Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard. German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were called Zeppelins; the first of which had its maiden flight in 1900. Regularly scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships were used as observation platforms and bombers during the war.
What is the answer to this question: What year was hydrogen filled balloons invented?
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So... 1783


Here is a question about this article: According to Thomas DeGregori, an economics professor at the University of Houston, in an article published by the Cato Institute, a libertarian think-tank operating in Washington D.C., "it is clear that technological and economic change are vital ingredients in getting children out of the workplace and into schools. Then they can grow to become productive adults and live longer, healthier lives. However, in poor countries like Bangladesh, working children are essential for survival in many families, as they were in our own heritage until the late 19th century. So, while the struggle to end child labour is necessary, getting there often requires taking different routes—and, sadly, there are many political obstacles.
What is the answer to this question: What are the obstacles he claims are to ending child labor?
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So... political obstacles


Here is a question about this article: Roman Catholic Jesuits and Capuchins arrived from Europe in the 17th and 18th centuries. Portuguese missionaries Jesuit Father António de Andrade and Brother Manuel Marques first reached the kingdom of Gelu in western Tibet in 1624 and was welcomed by the royal family who allowed them to build a church later on. By 1627, there were about a hundred local converts in the Guge kingdom. Later on, Christianity was introduced to Rudok, Ladakh and Tsang and was welcomed by the ruler of the Tsang kingdom, where Andrade and his fellows established a Jesuit outpost at Shigatse in 1626.
What is the answer to this question: When did Roman Catholic Jesuits and Capuchins arrive in Tibet from Europe?
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So...
17th and 18th centuries