【正文】 Yes,so thereare twokinds of limestone about 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 全國免費咨詢電話： 4000123267 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。 Butnot 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: 全國免費咨詢電話： 4000123267 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, th ink 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, 全國免費咨詢電話： 4000123267 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, theclari 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 an, 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 全國免費咨詢電話： 4000123267 pressingthe keysof a piano causestiny feltcoveredhammerstostrikethe strings insidethe instrument,likedrumsticksstriking the head ofa drum. Thisstriking action iswhy thepiano is percussion in