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.

Sentence: Some of the cleaner energy facilities in Boston include the Allston green district, with three ecologically compatible housing facilities. Boston is also breaking ground on multiple green affordable housing facilities to help reduce the carbon footprint of the city while simultaneously making these initiatives financially available to a greater population. Boston's climate plan is updated every three years and was most recently modified in 2013. This legislature includes the Building Energy Reporting and Disclosure Ordinance, which requires the city's larger buildings to disclose their yearly energy and water use statistics and partake in an energy assessment every five years. These statistics are made public by the city, thereby increasing incentives for buildings to be more environmentally conscious.
Question: How often is Boston's climate plan updated?
every three years