Plantsarechemicalfactories.Manyofthechemicalsthattheyproduceareusefultohumans.Besidesfoodplantsprovidematerialforpaperbuildingsmedicinesandmanyothers.Scientistsstudythechemicalstotreatcertaintypesofcancer.

Ontheotherhandthefastgrowthofthehumanpopulationischangingtheearthquickly.Onlybyunderstandinghowhumanactivitiesaffectourenvironmentcanwepredictglobalclimatechanges.Scientificstudiesofthesechangesandtheireffectonnaturalecosystemsandcropproductionareofgreatimportancetothefutureofoursociety.

Otherenvironmentalissuessuchaspollutionalsointerestscientists.Manyplantspeciesareespeciallysensitivetocertainpollutants.Scientistsstudytheeffectsofdifferenttypesofpollutiononplants.Theyusetheirresultstoadviselawmakerstomakelawsforenvironmentalprotectionandtosavepricelessnaturalareas.

Byusingplanttissueculture（植物细胞培养），scientistscangrowplantsfromsinglecells.Thishasexcitingpossibilitiesinbiotechnologyforestryandsoon.ForexampletheAmericanchestnutwasonceawidespreadtreeintheEasternforests.Todayithasnearlydisappearedbecauseofadisease-producingfungusthatcauseschestnuttodie.TheAmericanchestnutrecentlyhasbeengrowninplanttissueculture.

Theearth’sbiologicaldiversityorthekindsoflivingthingsaredecreasing.Ashumanschangetheenvironmentfortheirownpurposesplantsandanimalslivingintheseareasbecomeincreasinglyendangered．Scientistsworktoidentifyandunderstandnewplantspeciesespeciallyinsuchbiologicallyrichareasasrainforests.Perhapsaplantundiscoverednowwillbecomeanimportantfoodcrop.Thereareprobablymanyundiscoveredplantsthatproduceusefuldrugstocureortreathumandisease.Biologicaldiversityalsoprovidesanimportantsourceofnewgenestoimprovetheplantswenowuse.Astechniquesofgeneticengineeringimprovesowillourabilitytoimproveourplants.

1．Whichofthefollowingisnottrueaccordingtothispassage?

A．Allthechemicalsweneedareproducedbyplants.

B．Ifwecanunderstandhowhumanactivitiesaffectourenvironmentwecanpredictglobalclimatechanges.

C．Scienceplaysanimport