Here is a question about this article: European colonialism in the Sahara began in the 19th century. France conquered the regency of Algiers from the Ottomans in 1830, and French rule spread south from Algeria and eastwards from Senegal into the upper Niger to include present-day Algeria, Chad, Mali then French Sudan including Timbuktu, Mauritania, Morocco (1912), Niger, and Tunisia (1881). By the beginning of the 20th century, the trans-Saharan trade had clearly declined because goods were moved through more modern and efficient means, such as airplanes, rather than across the desert.
What is the answer to this question: During what time were good moved through more modern means?
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So... 20th century

Here is a question about this article: The tribes were ruled by clans (rod) consisting of people related by blood or marriage and theoretically descending from a common ancestor, giving the rod/clan a highly developed sense of solidarity. (See gens.) The starosta (or starszyna) had judicial and military power over the rod/clan, although this power was often exercised with an assembly of elders. Strongholds called grd were built where the religious cult was powerful, where trials were conducted, and where clans gathered in the face of danger. The opole was the territory occupied by a single tribe. (Manteuffel 1982, p. 44)
What is the answer to this question: What gave them a sense of solidarity?
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So... related by blood or marriage

Here is a question about this article: A very small amount of water vapor inside a light bulb can significantly affect lamp darkening. Water vapor dissociates into hydrogen and oxygen at the hot filament. The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp. Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle. The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening. Small amounts of substances such as zirconium are placed within the lamp as a getter to react with any oxygen that may bake out of the lamp components during operation.
What is the answer to this question: How does water vapor inside a light bulb affect lamp darkening?
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So...
significantly increase darkening