Context and question: To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again. This is the principle behind positive displacement pumps, like the manual water pump for example. Inside the pump, a mechanism expands a small sealed cavity to create a vacuum. Because of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed into the pump's small cavity. The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size.
Why is fluid in a manual pump pushed into the pumps cavity when a small sealed cavity is expanded?
Answer: Because of the pressure differential
Context and question: UN forces retreated to Suwon in the west, Wonju in the center, and the territory north of Samcheok in the east, where the battlefront stabilized and held. The PVA had outrun its logistics capability and thus were unable to press on beyond Seoul as food, ammunition, and materiel were carried nightly, on foot and bicycle, from the border at the Yalu River to the three battle lines. In late January, upon finding that the PVA had abandoned their battle lines, General Ridgway ordered a reconnaissance-in-force, which became Operation Roundup (5 February 1951). A full-scale X Corps advance proceeded, which fully exploited the UN Command's air superiority, concluding with the UN reaching the Han River and recapturing Wonju.
How was the PVA transporting supplies at one point?
Answer: on foot and bicycle
Context and question: There have been instances where a country's government bans a movie, resulting in the spread of copied videos and DVDs. Romanian-born documentary maker Ilinca Calugareanu wrote a New York Times article telling the story of Irina Margareta Nistor, a narrator for state TV under Nicolae Ceausescu's regime. A visitor from the west gave her bootlegged copies of American movies, which she dubbed for secret viewings through Romania. According to the article, she dubbed more than 3,000 movies and became the country's second-most famous voice after Ceausescu, even though no one knew her name until many years later.
What did a visitor give to Nistor?
Answer:
bootlegged copies of American movies