听力原文： If your boss asks you to work in Moscow this year, hed better offer you more money to do so — or even double that depending on where you live now. Thats because Moscow has just been found to be the worlds most expensive city for the second year in a row by Mercer Human Resources Consulting. Using the cost of living in New York as a base, Mercer determined Moscow is 34.4 percent more expensive including the cost of housing, transportation, food, clothing, household goods and entertainment. A two-bedroom flat in Moscow now costs $4,000 a month, a CD $24.83, and an international newspaper $6.30, according to Mercer. By comparison, a fast food meal with a hamburger is a steal at $4.80. London takes the No. 2 place up from No. 5 a year ago, thanks to higher cost of housing and a stronger British pound relative to the dollar. Mercer estimates London is 26 percent more expensive than New York these days. Following London closely are Seoul and Tokyo, both of which are 22 percent more expensive than New York, while No. 5 Hong Kong is 19 percent more costly. Among North American cities, New York and Los Angeles are the most expensive and are the only two listed in the top 50 of the worlds most expensive cities. But both have fallen since last years study — New York came in 15th, down from 10th place, while Los Angeles fell to 42nd from 29th place a year ago. San Francisco came in a distant third at No. 54, down 20 places from a year earlier. Toronto, meanwhile, is Canadas most expensive city but fell 35 places to take 82nd place worldwide. In Australia, Sydney is the priciest place to live in and No. 21 worldwide. Questions 19 to 21 are based on the passage you have just heard. 19. What made London become the second most expensive city? 20. Which city is the third most expensive on the list? 21. Which city has dropped most on the list in North America?19．