Here is a question about this article: DC systems (especially third-rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide. This may be a factor favouring overhead wires and high-voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained.
What is the answer to this question: Besides speed and size what else the low voltage of DC system can effect?
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So... air-conditioning


Here is a question about this article: In the high villages people live in homes built according to medieval designs that withstand cold winters. The kitchen is separated from the living area (called the stube, the area of the home heated by a stove), and second-floor bedrooms benefit from rising heat. The typical Swiss chalet originated in the Bernese Oberland. Chalets often face south or downhill, and are built of solid wood, with a steeply gabled roof to allow accumulated snow to slide off easily. Stairs leading to upper levels are sometimes built on the outside, and balconies are sometimes enclosed.
What is the answer to this question: What do people in high villages build their homes according to?
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So... medieval designs that withstand cold winters


Here is a question about this article: Rapid increases in a number of commodity prices followed the collapse in the housing bubble. The price of oil nearly tripled from $50 to $147 from early 2007 to 2008, before plunging as the financial crisis began to take hold in late 2008. Experts debate the causes, with some attributing it to speculative flow of money from housing and other investments into commodities, some to monetary policy, and some to the increasing feeling of raw materials scarcity in a fast-growing world, leading to long positions taken on those markets, such as Chinese increasing presence in Africa. An increase in oil prices tends to divert a larger share of consumer spending into gasoline, which creates downward pressure on economic growth in oil importing countries, as wealth flows to oil-producing states. A pattern of spiking instability in the price of oil over the decade leading up to the price high of 2008 has been recently identified. The destabilizing effects of this price variance has been proposed as a contributory factor in the financial crisis.
What is the answer to this question: What did the price of oil began doing when the financial crisis began to take hold in late 2008?
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So...
plunging