forfivedayshastotravelbetwee
zo
eseverydayWhattypeofticketwouldheprobablybuy
ASi
gle
BWeekly
COffpeakDaily
DTe
tripSaver
D
Haveyouever
oticedthecolourofthewateri
ariverorstreamafteraheavyrai
fallWhatdoyouthi
kcausedthischa
gei
colourItissoilthathasbee
washedi
totheriverfromtheriverba
korfromtle
earbyfields
Compo
e
tsofSoil
Soilismadeupofa
umberoflayers层eachhavi
gitsow
disti
ctivecoloura
dtextureTheupperlayerisk
ow
asthelitterItactslikeabla
ketlimiti
gtemperaturecha
gesa
dreduci
gwaterlossThetopsoillayerismadeupofsmallparticlesofrockmixedwithrotte
pla
ta
da
imalmattercalledhumus腐殖质whichisblacka
dgivesthetopsoilitsdarkcolourThislayerisusuallyrichi
utrie
tsoxyge
a
dwaterBelowthetopsoilisthesubsoilalayerthatco
tai
smoresto
esmixedwitho
lysmallamou
tsoforga
icmatterThislayerislighteri
colourbecauseofthelackofhumusBe
eaththesoilliesalayerofbedrock
SoilformsfromthebottomupOvertimebedrockisattackedbyrai
wi
dfrosta
ds
owItisgraduallybroke
dow
i
tosmallerparticlesi
aprocesscalledweatheri
gPla
tsbegi
togrowa
drotte
materialse
richthetopsoilMostofthesoili
Easter
Ca
adaforexampleWasformedfromweatheredrockthatwasexposedwhe
theicedisappearedl2000yearsago
WaterBe
eaththeSoil
fSurfacewatercollectsa
dflowsabovethegrou
di
lakespo
dsa
driversO
cei
thesoilorrockitiscalledgrou
dwaterGravitypullsgrou
dwaterthroughthesoili
aprocesscalledpercolatio
渗透Eve
tuallythewaterreachesalayercalledthewatertableU
derthisisbedrockthroughwhichwaterca
otpercolate
Aswaterpercolatesdow
warditdissolvesorga
icmattera
dmi
eralsfromthesoila
dcarriesthemtodeeperlayersThiscausesaseriousproblembecausepla
tsrequirethese
utrie
tsforgrowth
SoilpH
Soilca
beacidic
eutralorbasicThepHofthesoilisdetermi
edbythe
atureoftherockfromwhichitwasformeda
dbythe
atureofthepla
tsthatgrowa
droti
it
Theacidityofrai
a
ds
owca
lowerthepHofthegrou
dwaterthate
tersthesoilBybur
i
gfossilfuelssuchascoaloila
dgasoli
ehuma
shavebee
co
tributi
gtohigherlevelsofacidityi
ma
ysoilsWhe
fossilfuelsarebur
edgasesarereleasedi
totheaira
dthe
fallbacktoearthasacidrai
Acidsoili
creases出eproblemofcarryi
g
utrie
tstolowersoillevelsAs
utrie
tsareremovedsoilislessfertilePla
tsgrowmoreslowlyi
acidicsoila
dalsobecomeeasilyattackedbydiseases
67Thelayerofsoilthatprovides
ecessary
utrie
tsforpla
tgrowthiscalled
A1itter
Btopsoil
Chumus
Dsubsoil
68Accordi
gtothetextwhichofthefollowi
gisNOTtrue
ASoilformsfromweatheredrocko
theearthsurface
BThedeeperlayerofsoilr