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 Q]: Sentence: Seattle annually sends a team of spoken word slammers to the National Poetry Slam and considers itself home to such performance poets as Buddy Wakefield, two-time Individual World Poetry Slam Champ; Anis Mojgani, two-time National Poetry Slam Champ; and Danny Sherrard, 2007 National Poetry Slam Champ and 2008 Individual World Poetry Slam Champ. Seattle also hosted the 2001 national Poetry Slam Tournament. The Seattle Poetry Festival is a biennial poetry festival that (launched first as the Poetry Circus in 1997) has featured local, regional, national, and international names in poetry. 
Question: How often is the Seattle Poetry festival held?
[EX A]: biennial

[EX Q]: Sentence: In September 1695, Captain Henry Every, an English pirate on board the Fancy, reached the Straits of Bab-el-Mandeb, where he teamed up with five other pirate captains to make an attack on the Indian fleet making the annual voyage to Mocha. The Mughal convoy included the treasure-laden Ganj-i-Sawai, reported to be the greatest in the Mughal fleet and the largest ship operational in the Indian Ocean, and its escort, the Fateh Muhammed. They were spotted passing the straits en route to Surat. The pirates gave chase and caught up with Fateh Muhammed some days later, and meeting little resistance, took some £50,000 to £60,000 worth of treasure. 
Question: how often did the Indian fleet voyage to Mocha?
[EX A]: annual

[EX Q]: Sentence: The central part of the Sahara is hyperarid, with little to no vegetation. The northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis where moisture collects. In the central, hyperarid part, there are many subdivisions of the great desert such as the Tanezrouft, the Ténéré, the Libyan Desert, the Eastern Desert, the Nubian Desert and others. These absolute desert regions are characterized by their extreme aridity, and some years can pass without any rainfall. 
Question: How often does the Sahara go without rainfall?
[EX A]:
years