Here is a question about this article: Some international railway services to Continental Europe were operated during the 20th century as boat trains, such as the Admiraal de Ruijter to Amsterdam and the Night Ferry to Paris and Brussels. The opening of the Channel Tunnel in 1994 connected London directly to the continental rail network, allowing Eurostar services to begin. Since 2007, high-speed trains link St. Pancras International with Lille, Paris, Brussels and European tourist destinations via the High Speed 1 rail link and the Channel Tunnel. The first high-speed domestic trains started in June 2009 linking Kent to London. There are plans for a second high speed line linking London to the Midlands, North West England, and Yorkshire.
What is the answer to this question: When did local high speed rail service that linked London and Kent begin?
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So... June 2009

Here is a question about this article: Throughout the 20th century air defence was one of the fastest-evolving areas of military technology, responding to the evolution of aircraft and exploiting various enabling technologies, particularly radar, guided missiles and computing (initially electromechanical analog computing from the 1930s on, as with equipment described below). Air defence evolution covered the areas of sensors and technical fire control, weapons, and command and control. At the start of the 20th century these were either very primitive or non-existent.
What is the answer to this question: What was one of the quickest areas to evolve in military technology in the 20th century?
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So... air defence

Here is a question about this article: By the 1860s the Kingdom of Prussia and the Austrian Empire were the two most powerful nations dominated by German-speaking elites. Both sought to expand their influence and territory. The Austrian Empire like the Holy Roman Empire was a multi-ethnic state, but German-speaking people there did not have an absolute numerical majority; the creation of the Austro-Hungarian Empire was one result of the growing nationalism of other ethnicities especially the Hungarians. Prussia under Otto von Bismarck would ride on the coat-tails of nationalism to unite all of modern-day Germany. The German Empire ("Second Reich") was created in 1871 following the proclamation of Wilhelm I as head of a union of German-speaking states, while disregarding millions of its non-German subjects who desired self-determination from German rule.
What is the answer to this question: Who were the two most powerful nations in the 1860's?
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So...
Kingdom of Prussia and the Austrian Empire