佳选项，选项中有两项为多余选项。
Secretcodes密码keepmessagesprivate。Ba
kscompa
iesa
dgover
me
tage
ciesuse
17
fsecretcodesi
doi
gbusi
essespeciallywhe
i
formatio
isse
tbycomputer
Peoplehaveusedsecretcodesforthousa
dsofyears36Codebreaki
g
everlags落后farbehi
dcodemaki
gThescie
ceofcreati
ga
dreadi
gcodedmessagesiscalledcryptography
Therearethreemai
typesofcryptography37Forexamplethefirstlettersof“Myelepha
teatstooma
yeels”Spelloutthehidde
message“Meetme”
38Youmightreprese
teachletterwitha
umberforexampleLet’s
umberthelettersofthealphabeti
orderfrom1to26Ifwesubstitutea
umberforeachletterthemessage“Meetme”wouldread“13520135”
Acodeusessymbolstoreplacewordsphrasesorse
te
cesToreadthemessageofarealcodeyoumusthaveacodebook39Forexample“bridge”mightsta
dfor“meet”a
d“out”mightsta
dfor“me”Themessage“bridgeout”wouldactuallymea
“Meetme”
18
f40Howeveritisalsohardtokeepacodebooksecretforlo
gSocodesmustbecha
gedfreque
tly
AItisveryhardtobreakacodewithoutthecodebookBI
a
yla
guagesomelettersareusedmoretha
othersCO
lypeoplewhok
owthekeywordca
readthemessageDAslo
gastherehavebee
codespeoplehavetriedtobreakthemEYouca
hideamessagebyhavi
gthefirstlettersofeachwordspellitoutFWithacodebookyoumightwritedow
wordsthatwouldsta
dforotherwordsGA
otherwaytohideamessageistousesymbolstosta
dforspecificlettersofthealphabet第三部分英语知识运用（共两节，满分45分）第一节完形填空（共20小题；每小题15分，满分30分）
19
f阅读下面短文，从短文后各题所给的四个选项
（A、B、C和D）中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
A
Heroic
Driver
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gi
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g
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orthafterdeliveri
gtoo
eofhis42
Sudde
lyhesawacarwithitsbrightlightso

43hegotcloserhefou
d44vehicle
upsidedow
o
theroadO
emorelooka
dhe

oticed45shooti
goutfromu
derthe
46vehicleLarrypulledoversetthebrakea
d47thefireexti
guisher灭火器Two
goodburstsfromtheexti
guishera
dthefire
wasputout
Thema
whohadhisbrightlightso
48
a
dtoldLarryhehad49a
emerge
cy
callThey50heardawoma
’svoicecomi
gfromthewrecked毁坏的vehicle51
thevehicletheysawthatawoma
wastryi
gto
getoutofthebroke
wi
dowTheytoldherto
20
fstay52u
tiltheemerge
cyperso
elarrived53shethoughtthecarwasgoi
gto54Larrytoldherthathehadalreadyputoutthefirea
dsheshould
otmove55shei
juredher
eck
O
cefirea
demerge
cypeoplear