Onecauseofthecurrentfoodcrisisisdrought．FoodpricesarehighinpartbecauseofdryweatherinplacesasfardistantasSpainandAustralia．Aroundtheworldtheamountoflandaffectedbydroughthasdoubledinthepastthirtyyears．Andscientistsconcernedaboutclimatechangebelieveitwillcausemoredroughtinmanyareasinthefuture.

Alotofresearchisgoingintoeffortstodevelopdrought-resistantcrops．Oneprojectinvolvestobaccoplantsgeneticallyengineeredtokeeptheirleavesduringwatershortages．Theychosetobaccobecauseithasbigleaves．Alsoitgrowsfastandhasstructuralsimilaritieswithsomeotherplants.

Theresearchersdidanexperimentwithtwogroupsoftobaccoplants．Theyworkedwithasetofnormalplantsandasetoftransgenicplants．Thesehadageneaddedtointerferewiththebiologicalcausesofleaflossduringdrought.

Theresearchersputalltheplantsinagreenhousetogrowundernormalconditionsforfortydays．Thenforfifteendaysafterthattheplantsdidnotreceiveanywater.

Thenormalplantslosttheirgreencolor．Finallytheylosttheirleaves．Buttheresearcherssaythetransgenicplantskepttheirleavesandtheircolor.

Afterthefifteendrydaysalltheplantswerewateredagainforaweek．Thetransgenicplantsreturnedtonormalgrowthandtheirseedproductionwasclosetonormal．Buttheotherplantsalldied.

Inadditiontheresearchersfoundthattheplantscouldsurviveononlythirtypercentofthenormalamountofirrigationwater．Yieldlosswasminortheysaid.

Thefindingsappearedlate2007intheProceedingsoftheNationalAcademyofSciences．TheUniversityofCaliforniahasappliedforpatentprotectionforthetechnology.

TheresearchersexpecttomoveforwardwithfieldtestingofthetransgenictobaccoinlateAugust．Theyhopeforsimilarresultswithcropsliketomatoesricewheatandcotton.

71．ItcanbeinferredfromParagraph1that_______

A．theamountoflandaffectedbydroughthasdoubledinthepastthirtyyearsintheworld

B．droughtistheonlycausetoleadtothecurrentfoodcrisis.

C．foodpriceswillbehigherinthefuturewiththedroughtareasextending

D．foodpriceshasnothingtodowiththe