Here is a question about this article: The city's population increased more than sixfold during the first half of the 20th century, fed largely by an influx of European, Middle Eastern (Lebanese, Assyrian/Chaldean), and Southern migrants to work in the burgeoning automobile industry. In 1940, Whites were 90.4% of the city's population. Since 1950 the city has seen a major shift in its population to the suburbs. In 1910, fewer than 6,000 blacks called the city home; in 1930 more than 120,000 blacks lived in Detroit. The thousands of African Americans who came to Detroit were part of the Great Migration of the 20th century.
What is the answer to this question: How many blacks lived in Detroit in 1930?
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So... 120,000

Here is a question about this article: Nanjing is an important railway hub in eastern China. It serves as rail junction for the Beijing-Shanghai (Jinghu) (which is itself composed of the old Jinpu and Huning Railways), NanjingTongling Railway (Ningtong), NanjingQidong (Ningqi), and the Nanjing-Xian (Ningxi) which encompasses the HefeiNanjing Railway. Nanjing is connected to the national high-speed railway network by BeijingShanghai High-Speed Railway and ShanghaiWuhanChengdu Passenger Dedicated Line, with several more high-speed rail lines under construction.
What is the answer to this question: What line does Nanjing serve as a railway junction for?
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So... Beijing-Shanghai (Jinghu)

Here is a question about this article: Most copper is mined or extracted as copper sulfides from large open pit mines in porphyry copper deposits that contain 0.4 to 1.0% copper. Examples include Chuquicamata in Chile, Bingham Canyon Mine in Utah, United States and El Chino Mine in New Mexico, United States. According to the British Geological Survey, in 2005, Chile was the top mine producer of copper with at least one-third world share followed by the United States, Indonesia and Peru. Copper can also be recovered through the in-situ leach process. Several sites in the state of Arizona are considered prime candidates for this method. The amount of copper in use is increasing and the quantity available is barely sufficient to allow all countries to reach developed world levels of usage.
What is the answer to this question: What percentage of copper do the deposits have that are extracted?
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So...
0.4 to 1.0% copper