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: Uranium's average concentration in the Earth's crust is (depending on the reference) 2 to 4 parts per million, or about 40 times as abundant as silver. The Earth's crust from the surface to 25 km (15 mi) down is calculated to contain 1017 kg (2×1017 lb) of uranium while the oceans may contain 1013 kg (2×1013 lb). The concentration of uranium in soil ranges from 0.7 to 11 parts per million (up to 15 parts per million in farmland soil due to use of phosphate fertilizers), and its concentration in sea water is 3 parts per billion. 
Question: How many times more abundant than silver is uranium in the Earth's crust?

A: 40
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Q: Sentence: FC Barcelona had a successful start in regional and national cups, competing in the Campionat de Catalunya and the Copa del Rey. In 1902, the club won its first trophy, the Copa Macaya, and participated in the first Copa del Rey, losing 1–2 to Bizcaya in the final. Hans Gamper — now known as Joan Gamper — became club president in 1908, finding the club in financial difficulty after not winning a competition since the Campionat de Catalunya in 1905. Club president on five separate occasions between 1908 and 1925, he spent 25 years in total at the helm. One of his main achievements was ensuring Barça acquire its own stadium and thus generate a stable income. 
Question: How many times between 1908 and 1925 was Gamper president?

A: five
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Q: Sentence: Birds need to alter their metabolism in order to meet the demands of migration. The storage of energy through the accumulation of fat and the control of sleep in nocturnal migrants require special physiological adaptations. In addition, the feathers of a bird suffer from wear-and-tear and require to be molted. The timing of this molt - usually once a year but sometimes twice - varies with some species molting prior to moving to their winter grounds and others molting prior to returning to their breeding grounds. Apart from physiological adaptations, migration sometimes requires behavioural changes such as flying in flocks to reduce the energy used in migration or the risk of predation. 
Question: How often do birds molt?

A:
usually once a year
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