A、The cost of the two hundred items. B、The economic growth last year. C、The population of the cities. D、The fluctuations of the

Tokyo has replaced Moscow as the world’s most expensive city for expatriates, and Beijing has moved into the top 10, according to a global survey released Tuesday by consultants Mercer.
    The survey uses New York as the base city with an index of 100 points when comparing the cost of 200 items, including housing, transport, food, clothing, household goods and entertainment.
    Tokyo scores 143.7 points and is nearly three times as costly as the cheapest city, Johannesburg, which has an index score of 49.6. Tokyo is a major international finance center, houses the headquarters of several of the world’s largest investment banks and insurance companies, and serves as a hub for Japan’s transportation, publishing, and broadcasting industries. [20]During the centralized growth of Japan’s economy following World War II, many large firms moved their headquarters from cities such as Osaka (the historical commercial capital") to Tokyo, in an attempt to take advantage of better access to the government. This trend has begun to slow due to ongoing population growth in Tokyo and the high cost of living there.
    Osaka was in second place, making Japan the only country with two cities in the top 10, followed by Moscow in third, Geneva at four and Hong Kong fifth. Cities in the United States, China and the Middle East surged from last year. New York jumped from 22nd to eight place, Beijing is now ninth, up from 20th, while Dubai has climbed 32 places to number 20. London dropped 13 places from last year to be the 16th most expensive city in the world, while Paris slipped one spot to 13th, according to Mercer’s annual Cost of Living survey of 143 cities.
    [21] "As a direct impact of the economic downturn over the last year we have observed significant fluctuations in most of the world’s currencies, which have had a profound impact on this year’s ranking," said Nathalie Constantin-Metral, senior researcher at the consulting and investment services company.
    "Many currencies, including the Euro and British pound, have weakened considerably against a strong US dollar, causing a number of European cities to drop in the rankings" she said in a statement.
     [22]Due to the strengthening dollar, all US cities became more expensive. Los Angeles gained 32 places to 23rd and Washington is up 41 places to 66th. Most European cities became cheaper for expats, with Warsaw experiencing the most dramatic change, dropping from 35th to 113th place.
20. Why did the large firms in Japan move their headquarters to Tokyo after World War II?
21. What has greatly influenced the ranking this year according to the talk?
22. What would happen when the US dollar strengthened according to the talk?