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.  

Ex Input:
Sentence: In October 2009, the MoD was heavily criticized for withdrawing the bi-annual non-operational training £20m budget for the volunteer Territorial Army (TA), ending all non-operational training for 6 months until April 2010. The government eventually backed down and restored the funding. The TA provides a small percentage of the UK's operational troops. Its members train on weekly evenings and monthly weekends, as well as two-week exercises generally annually and occasionally bi-annually for troops doing other courses. The cuts would have meant a significant loss of personnel and would have had adverse effects on recruitment. 
Question: How often do the TA troops regularly train?

Ex Output:
weekly evenings and monthly weekends


Ex Input:
Sentence: A squab is the name given to the young of domestic pigeons that are destined for the table. Like other domesticated pigeons, birds used for this purpose are descended from the rock pigeon (Columba livia). Special utility breeds with desirable characteristics are used. Two eggs are laid and incubated for about 17 days. When they hatch, the squabs are fed by both parents on "pigeon's milk", a thick secretion high in protein produced by the crop. Squabs grow rapidly, but are slow to fledge and are ready to leave the nest at 26 to 30 days weighing about 500 g (18 oz). By this time, the adult pigeons will have laid and be incubating another pair of eggs and a prolific pair should produce two squabs every four weeks during a breeding season lasting several months. 
Question: How often are pigeons able to breed for the consumption process ?

Ex Output:
a prolific pair should produce two squabs every four weeks during a breeding season lasting several months


Ex Input:
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?

Ex Output:

every fourth year