E
Arainforestisanareacoveredbytalltr eeswiththetotalhighrainfallspreadingquiteequallythroughtheyearandthetemperaturerarelydippingbelowl6℃．Rainforestshaveagreateffectontheworldenvironmentbecausetheycantakeinheatfromthesunandadjusttheclimate．Withouttheforestcover，theseareaswouldreflectmoreheatintotheatmosphere，warmingtherestoftheworld.Losingtherainforestsmayalsoinfluencewindandrainfallpatterns，potentiallycausingcertainnaturaldisastersallovertheworld．
Inthepasthundredyears，humanshavebegundestr oyingrainforestsinsearchofthreemajorresources(资源)：landforcrops，woodforpaperandotherproducts，landforraisingfarmanimals．Thisactionaffectstheenvironmentasawhole．Forexample，alotofcarbondioxide(二氧化碳)intheaircomesfromburningtherainforests．Peopleobviouslyhaveaneedfortheresourceswegainfromcuttingtr eesbutwewillsuffermuchmorethanwewillbenefit.
Therearetwomainreasonsforthis．Firstly，whenpeoplecutd owntr ees，generallytheycanonlyusethelandforayearortwo．Secondly，cuttinglargesectionsofrainforestsmayprovideagoodsupplyofwoodrightnow，butinthelongrunitactuallyreducestheworld’swoodsupply．
Rainforestsareoftencalledtheworld’sdrugstore．Morethan25％ofthemedicinesweusetodaycomefromplantsinrainforests．However，fewerthanl％ofrainforestplantshavebeenexaminedfortheirmedicalvalue．Itisextr emelylikelythatourbestchancetocurediseasesliessomewhereintheworld’sshrinkingrainforests．
72．Rainforestscanhelptoadjusttheclimatebecausethey．
A．reflectmoreheatintotheatmosphere
B．bringabouthighrainfallthroughouttheworld
C．rarelycausethetemperaturetodroplowerthanl6℃
D．reducetheeffectofheatfromthesunontheearth
正确答案：D
