In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

[Q]: Why do birds possess gizzards?, Context: Like the reptiles, birds are primarily uricotelic, that is, their kidneys extract nitrogenous waste from their bloodstream and excrete it as uric acid instead of urea or ammonia through the ureters into the intestine. Birds do not have a urinary bladder or external urethral opening and (with exception of the ostrich) uric acid is excreted along with feces as a semisolid waste. However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. They also excrete creatine, rather than creatinine like mammals. This material, as well as the output of the intestines, emerges from the bird's cloaca. The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by joining cloaca, and females lay eggs from it. In addition, many species of birds regurgitate pellets. Males within Palaeognathae (with the exception of the kiwis), the Anseriformes (with the exception of screamers), and in rudimentary forms in Galliformes (but fully developed in Cracidae) possess a penis, which is never present in Neoaves. The length is thought to be related to sperm competition. When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent. The digestive system of birds is unique, with a crop for storage and a gizzard that contains swallowed stones for grinding food to compensate for the lack of teeth. Most birds are highly adapted for rapid digestion to aid with flight. Some migratory birds have adapted to use protein from many parts of their bodies, including protein from the intestines, as additional energy during migration.
[A]: contains swallowed stones for grinding food to compensate for the lack of teeth

[Q]: After treatment, HSV will leave the body or hide somewhere?, Context: Persistent infections occur because the body is unable to clear the organism after the initial infection. Persistent infections are characterized by the continual presence of the infectious organism, often as latent infection with occasional recurrent relapses of active infection. There are some viruses that can maintain a persistent infection by infecting different cells of the body. Some viruses once acquired never leave the body. A typical example is the herpes virus, which tends to hide in nerves and become reactivated when specific circumstances arise.
[A]: hide

[Q]: Where did Greece's green electricity sources come from?, Context: In 2008 renewable energy accounted for 8% of the country's total energy consumption, a rise from the 7.2% it accounted for in 2006, but still below the EU average of 10% in 2008. 10% of the country's renewable energy comes from solar power, while most comes from biomass and waste recycling. In line with the European Commission's Directive on Renewable Energy, Greece aims to get 18% of its energy from renewable sources by 2020. In 2013 and for several months, Greece produced more than 20% of its electricity from renewable energy sources and hydroelectric power plants. Greece currently does not have any nuclear power plants in operation, however in 2009 the Academy of Athens suggested that research in the possibility of Greek nuclear power plants begin.
[A]:
renewable energy sources and hydroelectric power plants