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: 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


[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?
[A]: years


[Q]: Sentence: On 6 April 2011, after his proposed "Plan for Stability and Growth IV" (PEC IV) was rejected by the Parliament, Prime Minister José Sócrates announced on national television that the country would request financial assistance from the IMF and the European Financial Stability Facility, as Greece and the Republic of Ireland had done previously. It was the third time that the Portuguese government had requested external financial aid from the IMF—the first occasion occurred in the late 1970s following the Carnation's Revolution. In October 2011, Moody's Investor Services downgraded nine Portuguese banks due to financial weakness. 
Question: How many times has Portugal requested external financial support?
[A]:
third