instruction:
Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
question:
Iron deficiency is the most common nutritional disorder affecting at least one third of world's population. Though anemia is common manifestation of iron deficiency, other effects of iron deficiency on various tissues, organs and systems are usually under recognized. Impaired brain development and cognitive, behavioural and psychomotor impairment are most worrisome manifestations of iron deficiency. Studies have demonstrated that some of these changes occurring during period of brain growth spurt (<2 years age) may be irreversible. Association of iron deficiency with febrile seizures, pica, breath holding spells, restless leg syndrome and thrombosis is increasingly being recognized. Impaired cell-mediated immunity and bactericidal function are generally noted in iron-deficient persons; however, the findings are inconsistent. Despite proven reversible functional immunological defects in vitro studies, a clinically important relationship between states of iron deficiency and susceptibility to infections remains controversial. Studies from malaria endemic regions have reported increased incidence of malaria in association with iron supplementation. These and some other aspects of iron deficiency are reviewed in this article.
answer:
Which deficiency is the cause of restless leg syndrome?


question:
MPEG-4 Part 14 is an instance of the more general ISO/IEC 14496-12:2004 (MPEG-4 Part 12: ISO base media file format) which is directly based upon the QuickTime File Format.
answer:
Which is the basis of MPEG-4 Part 14?


question:
A volcanic eruption in Iceland has sent ash across northern Europe. Airlines have stopped or changed the flights across the Atlantic Ocean, leaving hundreds of passengers stuck in airports. Grimsvotn is one of the largest and most active volcanoes in Europe. What makes Grimsvotn different is that it lies under a huge glacier of ice up to 12 metres thick. The hot volcano heats up the ice above it, which then forms a layer of water between glacier and the volcano, keeping it stable. As the water flows out from under the glacier, the pressure lifts. The lava from the volcano then comes up to the surface. This is exactly what is happening today. Now airlines have to make changes to their flights so as not to fly through the clouds of volcanic ash. According to KLM, one of Europe's biggest airlines, airplanes cannot go under the cloud or over it. Going through the cloud can result in ash getting stuck in the airplane's engines, causing damage to the plane. The eruption has also caused problems for animals in Iceland. The volcano left ash and sharp, glass-like rocks all over the countryside. Farmers are keeping their animals inside to stop them eating ash-covered grass or the sharp objects.
answer:

how many passengers were forced to stay in the airport?