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.  

Example input: Sentence: Namibia conducts a census every ten years. After independence the first Population and Housing Census was carried out in 1991, further rounds followed in 2001 and 2011. The data collection method is to count every person resident in Namibia on the census reference night, wherever they happen to be. This is called the de facto method. For enumeration purposes the country is demarcated into 4,042 enumeration areas. These areas do not overlap with constituency boundaries to get reliable data for election purposes as well. 
Question: How often does Namibia conduct a census?
Example output: every ten years
Example explanation: Census is generally conducted every ten years in most countries like Namibia.
Q: Sentence: The most catastrophic earthquakes we know of occurred in 31 BCE, 363, 749, and 1033 CE, that is every ca. 400 years on average. Destructive earthquakes leading to serious loss of life strike about every 80 years. While stringent construction regulations are currently in place and recently built structures are earthquake-safe, as of 2007[update] the majority of the buildings in Israel were older than these regulations and many public buildings as well as 50,000 residential buildings did not meet the new standards and were "expected to collapse" if exposed to a strong quake. Given the fragile political situation of the Middle East region and the presence there of major holy sites, a quake reaching magnitude 7 on the Richter scale could have dire consequences for world peace. 
Question: How often do earthquakes that lead to serious loss of life occur?
A:
every 80 years