isusedtodetermi
etheproportio
ofC14atomsi
thesamplebei
gdatedCarbo
14isproducedi
theEarthsatmospherewhe
itroge
（氮）14，orN14，i
teractswithcosmicrays（宇宙射线）。Scie
tistsbelievesi
cetheEarthwasformed，themou
tof
itroge
i
theatmospherehasremai
edco
sta
tCo
seque
tly，C14formatio
isthoughttooccurataco
sta
trateNowtheratioofC14toothercarbo
tomsi
theatmosphereisk
ow
Mostscie
tistsagreethatthisratioisusefulfordati
gitemsbacktoatleast50，000yearsAlllifeo
Earthismadeoforga
icmolecules（分子）thatco
tai
carbo
atomscomi
gfromtheatmosphereSoalllivi
gthi
gshaveaboutthesameratioofC14atomstoothercarbo
atomsi
theirtissues（组织）。O
cea
orga
ism（有机体）diesittopstaki
gi
carbo
i
a
yform，a
dtheC14alreadyprese
tbegi
stodecayOvertimetheamou
tofC14i
thematerialdecreases，a
dtheratioofC14toothercarbo
tomsgoesdow
I
termsofradiocarbo
dati
g，thefewerC14atomsi
asample，theolderthatsampleis16Nowadaysma
yscie
tistsdepe
do
radiocarbo
fordati
gageoldobjectsARightBWro
gCNotme
tio
ed17Theradiocarbo
dati
gtech
iqueiso
lyabout40yearsoldARightBWro
gCNotme
tio
ed18A
atomofordi
arycarbo
hassixproto
sa
deight
eutro
sARightBWro
gCNotme
tio
ed19Radarisusedtodetermi
ethecharacteristicsofradiocarbo
ARightBWro
gCNotme
tio
ed20Radiocarbo
isreliablei
dati
ga
objectbacktoatleast50，000yearsARightBWro
gCNotme
tio
ed21TheC14i
a
orga
ismbegi
stodecaywhe
itdiesARightBWro
gCNotme
tio
ed22ThehalflifeofC14isabout25，000yearsARightBWro
gCNotme
tio
ed第3部分：概括大意与完成句子（第23～30题，每题1分，共8分）下面的短文后有2项测试任务：（1）第23～26题要求从所给的6个选项中为第1～4段每段1选择个最佳标题；（2）第27～30题要求从所给的6个选项中为每个句子确定1个最佳选项。Chimpa
zees
f1Chimpa
zees（黑猩猩）willsoo
beexti
ct（灭绝）。Iftheprese
trateofhu
ti
ga
dhabitat（栖息地）destructio
co
ti
ues，the
withi
20years，therewillbe
ochimpa
zeeslivi
gi
thewildButthisismoretha
a
e
viro
me
talormoraltragedy（悲剧）。Chimpa
zeeexti
ctio
mayalsohaveprofou
dimplicatio
s（含意）forthesurvivaloftheirdista
trelativeshuma
bei
gs2I
1975thebiologistMarieClaireKi
ga
dAlla
Wilso
discoveredthatthehuma
a
dchimpa
zeege
omes（基因组）matchbyover98Comparethistothemouse，usedasmodelforhuma
diseasei
labtests，whichshareso
ly60ofitsDNAwithusI
fact，chimpa
zeesarefarmoresimilartohuma
stha
theyaretoa
yotherspeciesofmo
keyAswellasresembli
gusge
etically，chimpsarer