Text 4 The Big Mac index is built on the idea of purchasing-power parity,the theory that in the long run currencies will converge until the same amount of money buys the same amount of goods and services in every country.A Big Mac cunently costs$5.06 in America but just 10.75 lira（$2.75）in Turkey,implying that the lira is undenalued.However,ot:her currencies are even cheaper.In Big Mac tenns,the Mexican peso is underval-ued by 55.9%against the greenback.Last week it also hit a record low as Mr Trump restated some of his campaign threats against Mexico.The peso has lost a tenth of iLs value against the dollar since November.Of big countries,only Russia offers a cheaper Big Mac,in dollar terms,even though the rouble has strengthened over the past year.The euro zone is also prey to political uncerLainty.Elections are scheduled this year in the Netherlands,France and Germany,and possible in Italy.The euro recently fell to its lowest level since 2003.Britain's Brexit vote has had an even bigger effect on the pound,which has fallen to$1.21,a 31-year low.According to the Big Mac index,the euro and the pound are undervalued against the dollar by 19.7%and 26.3%,respectively.One of the drawbacks of the Big Mac index is that it takes no account of labour costs.It should surprise no one that a Big Mac costs less in Shanghai than it does in San Francisco,since Chinese workers eam far less than their American counterparts.So in a slightly more sophisticated version of the Big Mac index,we take account of a country's average income.Hisiorically,this adjustment has tended to raise currencies'valuations against the dollar,so emerging-market currencies tend to look more reasonably priced.The Chinese yuan,for example,is 44%undervalued against the doUar according to our baseline Big Mac index,but only 7%according to the adjusted one.The deluxe Big Mac index has typically made rich-world currencies look more expensive.Because western Europeans have higher costs of Iiving and lower incomes than Americans,the euro has traded at around a 25%premium against the dollar in income-adjusted burger terms since Lhe euro's inception.But what once seemed to be a constant truth of burgemomics is true no longer.So strong is the dollar Lhat even the adjusted Big Mac index finds the euro undenalued.The dollar is now Uading at a 14-year high in trade-weighted terms.Emerging-world economies may struggle to pay off dollar denominated debts.American firms may find themselves at a disadvantage agzunst foreign competition.And American tourists will get more burgers for their buck in Europe.We can leam from Paragraph 3 that______
A.political uncertainty will not affect European countries
B.economic depression is the real reason for euro's devaluation
C.the value of currency is completely decided by domestic factors
D.the devaluation of the pound is mainly caused by Britain's policy
