【正文】 ut 90percent ofthem, you　　have waterfrom the surface,streams,waterfall or whatever movingwater that　　flowsthrough cracks found in limestone. It’s themoving wateritself that wearsaway　　at the rock and ,in surfacewater,there isa weak acid,　　carbonic acid, not sulfuricacid but carbonic acid that helpsdissolvethe rock. Witha　　littlehelpfrom this carbonic acid, movingwater formsmostof theworld’s limestone　　caves. WhenI wasresearchingthis fora study a fewyears ago, I visiteda coupleof　　thesetypical limestonecaves,and theywereall very wet,you know, from streams　　and rivers. Thisflowing watercarved out the cavesand thestructures insidethem.　　Male student?！　utnot Lechuguilla?　　Professor:　　Dry asa bone. Well,that mightbe a bit ofan exaggeration. Butit’ssafeto say that its　　sulfuricacid and not moving waterthat formedLechuguilla caveand thosefew other　　oneslikeit. In fact,there isno evidencethat flowing waterhas even gone inor out　　ofthe cave. So, it islikea passageways allaround. Thereare wide　　passages,narrow onesat all differentdepths, likeunderground tunnelsin the　　, sincethey werecreatedunderground and not from flowingsurface　　water,not all thesepassageways have an opening to the … and　　thereis otherevidence that flowing waterwasnot involved in 　　saidthat sulfuric aciddissolveslimestone,right, and formsthepassageways? What　　elsedoessulfuricacid do? Paul?　　Male student:　　Ah, leavesa chemicalresidue and…　　Femalestudent:　　Gypsum,right?　　Professor:　　Yep, you willfind lotsof gypsum deposited at , as weknow,gypsum　　issolublein if therewereflowing waterin thecave, it woulddissolvethe　　gypsum. Thisispart of whatled usto the realization that Lechuguillaisin that small　　group of waterlesscaves. And Lechuguillaispretty much dormant is not　　really forming any , thereisother oneslikeit, forexample, in Mexico,that　　are forming. And whencave researchersgo to explorethem,they seeand smell,the　　sulfuricacid and gasesof… er… phew… now,something else, think of rotteneggs.　　And, itis not justthe needto wearspecialmasksto protect　　themselvesfrom the gasesin ? Paul?　　Male student:　　Yeah, how about whatthesecaves look likeon the inside?　　Professor:　　Well,the formations… thereis reallysomething. Thereis suchvariety there like　　nothing anywhere elsein the world,someofthem areelaborate looking, like　　decorations. And a lotof them are madeofgypsum and could be up to 20feet long.　　It ispretty impressive.　　Lecture2　　Narrator:　　Listen to part ofa lecturein a music history class.　　Professor:　　Up untilnow inour discussions and readings about the broken early classicalperiods,　　wehave been talking about the development ofmusicalstylesand genreswithinthe　　relativelynarrow social contextof itspatronage by the upper classes. Composers,　　afterall, had to earna living and those whowereemployedin the servicesof a　　specificpatron, well,I do not have to spellitout for you, the likesand dislikesof that　　patron, this wouldhave had and effecton what wasbeing posedand performed.　　Now,of course,there weremanyother influenceson posers, um,such asthe　　technicaladvanceswehave seenin the development ofsomeof theinstruments, uh,　　you remember thetransverse flute, theclarinet and soon.　　ButI think if Iwereasked toidentify a singlecrucialdevelopmentin European music　　ofthis time, itwould bethe inventionof the piano, which,interestingly enough also　　had a significant effecton European society ofthat time. And I’llget to that ina　　,as weknow,keyboard instrumentsexisted long beforethepiano the　　organ, which datesback tothe Middle Ages,asdo other keyboard instruments,such　　as theharpsichord which isstillpopular today with somemusicians. Butnone of　　thesehas had asprofound an impactas thepiano.　　Um,thepiano wasinventedin Italy in1709. The word piano isshort forpianoforte, a　　bination ofthe Italianwords forsoftand loud. Now,unlikethe harpsichord　　whichcamebeforeit, the piano isa percussioninstrument. You see,theharpsichord　　isactually classifiedas a stringinstrument, sincepressing a key ofa harpsichord　　causesa tiny quillthat isconnected to thekey to pluck the stringsthat are inside the　　instrument, muchthat sameas a guitar pick plucksthe stringsof a guitar. But　　pressingthe keysof a piano causestiny feltcoveredhammerstostrikethe strings　　insidethe instrument,likedrumsticksstriking the head ofa drum. Thisstriking action　　iswhy thepiano is percussion instrument instead ofa str