Detailed Instructions: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Q: Passage: Throughout most of its history, Istanbul has ranked among the largest cities in the world. By 500 CE, Constantinople had somewhere between 400,000 and 500,000 people, edging out its predecessor, Rome, for world's largest city. Constantinople jostled with other major historical cities, such as Baghdad, Chang'an, Kaifeng and Merv for the position of world's most populous city until the 12th century. It never returned to being the world's largest, but remained Europe's largest city from 1500 to 1750, when it was surpassed by London.The Turkish Statistical Institute estimates that the population of Istanbul Metropolitan Municipality was 14,377,019 at the end of 2014, hosting 19 percent of the country's population. Then about 97–98% of the inhabitants of the metropolitan municipality were within city limits, up from 89% in 2007 and 61% in 1980. 64.9% of the residents live on the European side and 35.1% on the Asian side. While the city ranks as the world's 5th-largest city proper, it drops to the 24th place as an urban area and to the 18th place as a metro area because the city limits are roughly equivalent to the agglomeration. Today, it forms one of the largest urban agglomerations in Europe, alongside Moscow. The city's annual population growth of 3.45 percent ranks as the highest among the seventy-eight largest metropolises in the Organisation for Economic Co-operation and Development. The high population growth mirrors an urbanization trend across the country, as the second and third fastest-growing OECD metropolises are the Turkish cities of İzmir and Ankara.
Istanbul experienced especially rapid growth during the second half of the 20th century, with its population increasing tenfold between 1950 and 2000. This growth in population comes, in part, from an expansion of city limits—particularly between 1980 and 1985, when the number of Istanbulites nearly doubled. The remarkable growth was, and still is, largely fueled by migrants from eastern Turkey seeking employment and improved living conditions. The number of residents of Istanbul originating from seven northern and eastern provinces is greater than the populations of their entire respective provinces; Sivas and Kastamonu each account for more than half a million residents of Istanbul. Istanbul's foreign population, by comparison, is very small, 42,228 residents in 2007. Only 28 percent of the city's residents are originally from Istanbul. The most densely populated areas tend to lie to the northwest, west, and southwest of the city center, on the European side; the most densely populated district on the Asian side is Üsküdar.
A:
Where are the migrants coming from that fuel the growth of the city that is number one in OCED growth?