Problem: Airport construction boomed during the 1960s with the increase in jet aircraft traffic. Runways were extended out to 3,000 m (9,800 ft). The fields were constructed out of reinforced concrete using a slip-form machine that produces a continual slab with no disruptions along the length. The early 1960s also saw the introduction of jet bridge systems to modern airport terminals, an innovation which eliminated outdoor passenger boarding. These systems became commonplace in the United States by the 1970s.
How far were jet bridge systems extended to?
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Answer: unanswerable

Problem: In 1469, following the Treaty of St. Omer, Upper Alsace was sold by Archduke Sigismund of Austria to Charles the Bold, Duke of Burgundy. Although Charles was the nominal landlord, taxes were paid to Frederick III, Holy Roman Emperor. The latter was able to use this tax and a dynastic marriage to his advantage to gain back full control of Upper Alsace (apart from the free towns, but including Belfort) in 1477 when it became part of the demesne of the Habsburg family, who were also rulers of the empire. The town of Mulhouse joined the Swiss Confederation in 1515, where it was to remain until 1798.
When did Belfort join the Swiss Confederation?
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Answer: unanswerable

Problem: Bacteria often attach to surfaces and form dense aggregations called biofilms or bacterial mats. These films can range from a few micrometers in thickness to up to half a meter in depth, and may contain multiple species of bacteria, protists and archaea. Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures, such as microcolonies, through which there are networks of channels to enable better diffusion of nutrients. In natural environments, such as soil or the surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. Biofilms are also important in medicine, as these structures are often present during chronic bacterial infections or in infections of implanted medical devices, and bacteria protected within biofilms are much harder to kill than individual isolated bacteria.
What is part of secondary structure in the complex formation of bacteria?
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Answer:
microcolonies,