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 two became friends, and for many years lived in close proximity in Paris, Chopin at 38 Rue de la Chaussée-d'Antin, and Liszt at the Hôtel de France on the Rue Lafitte, a few blocks away. They performed together on seven occasions between 1833 and 1841. The first, on 2 April 1833, was at a benefit concert organized by Hector Berlioz for his bankrupt Shakespearean actress wife Harriet Smithson, during which they played George Onslow's Sonata in F minor for piano duet. Later joint appearances included a benefit concert for the Benevolent Association of Polish Ladies in Paris. Their last appearance together in public was for a charity concert conducted for the Beethoven Memorial in Bonn, held at the Salle Pleyel and the Paris Conservatory on 25 and 26 April 1841. 
Question: How many times did Chopin and Liszy perform together in public?
A:
seven