阅读理解
Noneofourearlyancestorscoulddigestmilkasadultsbecausetheirbodiesneverhadto-milkdrinkingsimplywasn'tanoption.Aspeoplebegantoextractmilkfromanimalsthoughsomepeopledevelopedthe
abilitytokeepdrinkingitthroughouttheirlives.
Scientistsnowknowofamilkrelatedmutation(变异)inourgenes-thechemicalinstructionsforlifethatwecarryinalmosteverycellinourbodies.Peoplewhohaveamutatedformofoneparticulargenecan
drinkmilkjustfine.Peoplewithoutthemutationtendtogetsickfrommilk.
Tofigureoutwhereandpossiblywhymilkdrinkingstartedsomescientistshavebeenlookingatwho
hasthemilkdigestingmutationtoday.Patternsarestriking.
MostadultsinNorthernandCentralEuropeareabletodigestmilk-andtheydo.Cheesebutterand
otherdairyproductsarepopularincountriessuchasSwedenDenmarkGermanyandEngland.Because
EuropeansettlersdominatedNorthAmericamostpeopleherecanhandlemilkjustfineaswell.Thatmay
explainwhyicecreamissuchapopulardessertintheUnitedStates.
InmuchofAfricaAsiaandSouthAmericaontheotherhandpeopletendtoavoiddairyproducts
becausetheyleadtodiarrhea(腹泻)andotherstomachproblems.(That'swhyyouwon'ttypicallyfind
cheeseonthemenuataChineseJapaneseorEthiopianrestaurant.)NativeAmericansarealsounableto
digestmilk.
BasedonthesegeneticpatternsscientistshavelongthoughtthatmilkdrinkingstartedinNorthern
Europewheredairyisaninstitutionandthemilkdigestingmutationiseverywhere.
Arecentstudypaintedadifferentpicture.WithacomputermodelThomasandcolleagueslookedatthespreadofthemilkdrinkingmutationfarmingandotherrelatedfactors.Workingbackwardthescientists
concludedthatthefirstmilkdrinkerslivedinCentralEuropearoundwhat'snowHungaryabout7500
yearsago.Thepracticedidn'tstartfarthernorthasscientistshadthoughtbefore.
1.Whichofthefollowingistheproperorderofeventsaccordingtothepassage?
a.Theirchildrenwereabletodigestmilkasadults.
b.Theygotsickfromthem