题目内容：
回答题：RuiningtheRuins
Acidrain（酸雨）isnowafamiliarproblemintheindustrializedcountriesinEurope.Harmfulgasesareproducedbypowerstationsandcars.Theydissolveinrainwaterandthismakesacidrain,whichdamagestrees,riversandstreams.
Acidrainisalsocapableofdissolvingsomerocks.Andbuildingsmadeofsoftrock,suchaslimestone（石灰石）,areparticularlybadlyaffected.Theacidrainattackstherock,andsocarvingsandstatuesareeroded（受腐蚀）morequickly.
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（46）AccordingtoareportintheNewScientist,acidrainisbeingblamedfortherapiddecayofancientruinsinMexico.TheoldlimestonebuildingsinplaceslikeChichenItza,TulumandPalenquearewearingawayveryquicklyindeed.ThesesitesaretheremainsofthebuildingsbuiltbytheMayasbetween250BCandAD900,andthespectacularruinsofMayancivilizationarevisitedbythousandsoftouristseveryyear. Butthoseruinsareindangerofbeingseriouslydamagedbypollution.Atmanysitesthestonehasbeencoveredwithalayerofblacksubstance.________________（47）Scientistsestimatethataboutonemillimeterofstoneiswornawayeverytwelveyears.________________（48）TheacidrainissaidtobecausedbypollutionfromoilwellsintheGulfofMexico.Carexhaustgasesarealsoaproblem.Localvolcaniceruptionsmaketheproblemevenworse.Nevertheless,withenoughmoneyandeffort,researcherssaythatmanyoftheproblemscouldbesolvedandtherateoferosionreduced.____________（49）. Mexico’scurrentlackoffundsisalsopartlyduetooil.Thecountryhasrichoil fields and a few years ago, when oil was expensive, Mexico was selling large quantities of oil to the USA and earning a lot of money. __________ (50) However, the price of oil then dropped, and Mexico has been left owing enormous sums of money and with not enough income from oil sales to pay back the loans. So unless the price of oil rises, it is unlikely that Mexico will be able to afford to clean up the pollution and save its Mayan ruins from destruction.
A．At others the painted surfaces inside temples are lifting and flaking off () and the stone is being eaten away.
B．That is enough to have caused some of the ancient carvings to become seriously damaged already.
C．These measures would reduce the pollution, but would not stop it completely.
D．The government was therefore able to borrow huge sums of money from banks around the world, thinking they would have no problem repaying their debts.
E．The problem, however, is not just a European one.
F．However, the Mexican government does not have enough money to do the work, and needs to spend what money it has on the Mexican people.
(46)__________
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