Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage

The Emergence of Megacities

The urban shift over time has led to the emergence of the megacity – a city with a population of 10 million or more. New York City and Tokyo were the first (21) .......... megacities, both (22) .......... an urban population of over 10 million by the 1950s. But today they are (23) .......... alone in their size. In 2014, there were 28 megacties across the planet – from Sao Paulo, Brazil to Lagos, Nigeria and London, England to Shanghai, China – and all major global regions except Oceania are (24) .......... with megacities.

Most of the megacities in recent years are located in Asia and Africa. In fact, it is where seven of wight newest megacities can be found and where 10 of the 12 (25) .......... megacities in 2030 will be located. From 2010 to 2015, Kinshasa’s population grew (26) .......... over 23 percent, and today over half of 11.6 million residents are under 22 years old. A (27) .......... of factors has led to this growth including migration from rural areas, high fertility rates, and widening of the city’s boundaries. The population is (28) .......... almost all support structure in the city (29) .......... the threat of food shortages, traffic (30) .........., and insufficient education facilities have become an obvious reality.

(21) ..............

• A. 
  knew
• B. 
  known
• C. 
  familiar
• D. 
  acquainted