A study comparing prices in 150 major cities has found that cities in Western Europe have become more expensive to live in since the full introduction of the euro currency (货币). The report also noted a fall in living costs in cities where there are economic (经济的) or political problems such as Buenos Aires in Argentina and Harare in Zimbabwe. The findings are shown in the latest worldwide cost of living study conducted yearly by the Economist Intelligence Unit, a business research organization based in London. The information is meant to help big firms set payments for people working away from their home country. As in last year's study, two Japanese cities, Tokyo and Osaka, were found to be the most expensive places to live. The report also says that cities in the euro zone (欧元区) , have become more expensive relative to other places since the introduction of euro notes and coins. For example, Paris now has the tenth highest costs it was in fourteenth place a few years ago. Berlin has gone from fiftieth to thirty-first place. Those findings will strengthen the opinion that businesses have exploited disorder over the new currency to push up their prices. But as in past years, the highest costs in Europe are outside the euro zone. London, for example, is the seventh most expensive city in the world to live in. New York, which has the highest prices in America, is in 11th place. The biggest fall in relative costs has taken place in Buenos Aires. That partly shows the fall of the Argentine currency, following the country's inability to pay the money it owes. The cheapest major cities were found to be Tehran in Iran and Harare, capital of Zimbabwe. What is the text mainly about?