instruction:
This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
question:
Karlheinz Brandenburg used a CD recording of Suzanne Vega's song "Tom's Diner" to assess and refine the MP3 compression algorithm. This song was chosen because of its nearly monophonic nature and wide spectral content, making it easier to hear imperfections in the compression format during playbacks. Some refer to Suzanne Vega as "The mother of MP3". This particular track has an interesting property in that the two channels are almost, but not completely, the same, leading to a case where Binaural Masking Level Depression causes spatial unmasking of noise artifacts unless the encoder properly recognizes the situation and applies corrections similar to those detailed in the MPEG-2 AAC psychoacoustic model. Some more critical audio excerpts (glockenspiel, triangle, accordion, etc.) were taken from the EBU V3/SQAM reference compact disc and have been used by professional sound engineers to assess the subjective quality of the MPEG Audio formats.
answer:
What type of recording did Brandenburg use?


question:
Seattle's economy is driven by a mix of older industrial companies, and "new economy" Internet and technology companies, service, design and clean technology companies. The city's gross metropolitan product was $231 billion in 2010, making it the 11th largest metropolitan economy in the United States. The Port of Seattle, which also operates Seattle–Tacoma International Airport, is a major gateway for trade with Asia and cruises to Alaska, and is the 8th largest port in the United States in terms of container capacity. Though it was affected by the Great Recession, Seattle has retained a comparatively strong economy, and remains a hotbed for start-up businesses, especially in green building and clean technologies: it was ranked as America's No. 1 "smarter city" based on its government policies and green economy. In February 2010, the city government committed Seattle to becoming North America's first "climate neutral" city, with a goal of reaching zero net per capita greenhouse gas emissions by 2030.
answer:
What was Seattle's gross product in 2010?


question:
The most important existing communal shelters were the London Underground stations. Although many civilians had used them as such during the First World War, the government in 1939 refused to allow the stations to be used as shelters so as not to interfere with commuter and troop travel, and the fears that occupants might refuse to leave. Underground officials were ordered to lock station entrances during raids; but by the second week of heavy bombing the government relented and ordered the stations to be opened. Each day orderly lines of people queued until 4 pm, when they were allowed to enter the stations. In mid-September 1940 about 150,000 a night slept in the Underground, although by the winter and spring months the numbers had declined to 100,000 or less. Noises of battle were muffled and sleep was easier in the deepest stations, but many were killed from direct hits on several stations.
answer:

Why did the government refuse to allow the London Underground stations to be used as shelters?