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.  

Q: Sentence: Boston has a strong mayor – council government system in which the mayor (elected every fourth year) has extensive executive power. Marty Walsh became Mayor in January 2014, his predecessor Thomas Menino's twenty-year tenure having been the longest in the city's history. The Boston City Council is elected every two years; there are nine district seats, and four citywide "at-large" seats. The School Committee, which oversees the Boston Public Schools, is appointed by the mayor. 
Question: How often are elections for mayor held in Boston?

A: every fourth year
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Q: Sentence: In presidential elections, Montana was long classified as a swing state, though the state has voted for the Republican candidate in all but two elections from 1952 to the present. The state last supported a Democrat for president in 1992, when Bill Clinton won a plurality victory. Overall, since 1889 the state has voted for Democratic governors 60 percent of the time and Democratic presidents 40 percent of the time, with these numbers being 40/60 for Republican candidates. In the 2008 presidential election, Montana was considered a swing state and was ultimately won by Republican John McCain, albeit by a narrow margin of two percent. 
Question: How often has Montana voted for a Democratic governor?

A: 60 percent
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Q: Sentence: Spring and autumn have, on average, mild days and fresh nights but are changing and unstable. Surprisingly warm or cool weather occurs frequently in both seasons. In winter, sunshine is scarce; days are cold but generally above freezing with temperatures around 7 °C (45 °F). Light night frosts are however quite common, but the temperature will dip below −5 °C (23 °F) for only a few days a year. Snow falls every year, but rarely stays on the ground. The city sometimes sees light snow or flurries with or without accumulation. 
Question: How often does the temperature drop below -5 C

A:
a few days a year
****