Problem: By the 1840s, India was no longer capable of supplying the vast quantities of cotton fibers needed by mechanized British factories, while shipping bulky, low-price cotton from India to Britain was time-consuming and expensive. This, coupled with the emergence of American cotton as a superior type (due to the longer, stronger fibers of the two domesticated native American species, Gossypium hirsutum and Gossypium barbadense), encouraged British traders to purchase cotton from plantations in the United States and plantations in the Caribbean. By the mid-19th century, "King Cotton" had become the backbone of the southern American economy. In the United States, cultivating and harvesting cotton became the leading occupation of slaves.
What was the difference that made American cotton preferred over Indian cotton?
The answer is the following: longer, stronger fibers

Problem: Early reports of Europeans reaching this area include those of the Venetian Alvise Cadamosto's voyage of 1455, the 1479–1480 voyage by Flemish-French trader Eustache de la Fosse, and Diogo Cão. In the 1480s this Portuguese explorer reached the Congo River and the lands of Bakongo, setting up the foundations of modern Angola, some 4200 km down the African coast from Guinea-Bissau.
What river did Diogo Cao reach in the 1480's?
The answer is the following: Congo River

Problem: Zinc chemistry is similar to the chemistry of the late first-row transition metals nickel and copper, though it has a filled d-shell, so its compounds are diamagnetic and mostly colorless. The ionic radii of zinc and magnesium happen to be nearly identical. Because of this some of their salts have the same crystal structure and in circumstances where ionic radius is a determining factor zinc and magnesium chemistries have much in common. Otherwise there is little similarity. Zinc tends to form bonds with a greater degree of covalency and it forms much more stable complexes with N- and S- donors. Complexes of zinc are mostly 4- or 6- coordinate although 5-coordinate complexes are known.
What is the determining factor where zinc and magnesium are very similar chemically?
The answer is the following: ionic radius

Problem: The southern Essonne department specialises in science and technology, and the south-eastern Val-de-Marne, with its wholesale Rungis food market, specialises in food processing and beverages. The Paris region's manufacturing decline is quickly being replaced by eco-industries: these employ about 100,000 workers. In 2011, while only 56,927 construction workers worked in Paris itself, its metropolitan area employed 246,639, in an activity centred largely around the Seine-Saint-Denis (41,378) and Hauts-de-Seine (37,303) departments and the new business-park centres appearing there.
How many construction workers worked in Paris in 2011?
The answer is the following:
56,927