TASK DEFINITION: In this task, you're given passages that contain mentions of a time duration related quesry and we are supposed to write answer to a question that involves event “frequency", which refers to how often an event is likely to be repeated. For example, "taking showers" typically occurs ~5 times a week, "going to saturday market" usually happens every few weeks/months, etc. 
 Note that a lot of the questions could have more than one correct answers. We only need a single most-likely answer. Please try to keep your "answer" as simple as possible. Concise and simple "answer" is preferred over those complex and verbose ones.  
PROBLEM: Sentence: Numerous recordings of Chopin's works are available. On the occasion of the composer's bicentenary, the critics of The New York Times recommended performances by the following contemporary pianists (among many others): Martha Argerich, Vladimir Ashkenazy, Emanuel Ax, Evgeny Kissin, Murray Perahia, Maurizio Pollini and Krystian Zimerman. The Warsaw Chopin Society organizes the Grand prix du disque de F. Chopin for notable Chopin recordings, held every five years. 
Question: The Warsaw Chopin Society holds the Grand prix du disque de F. Chopin how often?

SOLUTION: every five years.

PROBLEM: Sentence: To clean up pollution, the federal and local governments implemented numerous plans including the constant monitoring and reporting of environmental conditions, such as ozone and nitrogen oxides. When the levels of these two pollutants reached critical levels, contingency actions were implemented which included closing factories, changing school hours, and extending the A day without a car program to two days of the week. The government also instituted industrial technology improvements, a strict biannual vehicle emission inspection and the reformulation of gasoline and diesel fuels. The introduction of Metrobús bus rapid transit and the Ecobici bike-sharing were among efforts to encourage alternate, greener forms of transportation. 
Question: How often do citizens need to get their cars examined?

SOLUTION: biannual

PROBLEM: Sentence: Sometimes circumstances such as a good breeding season followed by a food source failure the following year lead to irruptions in which large numbers of a species move far beyond the normal range. Bohemian waxwings Bombycilla garrulus well show this unpredictable variation in annual numbers, with five major arrivals in Britain during the nineteenth century, but 18 between the years 1937 and 2000. Red crossbills Loxia curvirostra too are irruptive, with widespread invasions across England noted in 1251, 1593, 1757, and 1791. 
Question: How many times did Bohemian waxwings come to Britain in the nineteeth century?

SOLUTION:
five