题目内容：
回答题：TheBodyClock
WhyisitthatflyingtoNewYorkfromLondonwillleaveyoufeelinglesstiredthanflyingtoLondonfromNewYork?Theanswermaybeaclearcaseofbiologynotbeingabletokeepupwithtechnology.Deepinsidethebrainthereisa‘clock’thatgovernseveryaspectofthebody’sfunctioning:sleepandwakecycles,levelsofalertness,performance,mood,hormonelevels,digestion,bodytemperatureandsoon.Itregulatesallofthesefunctionsona24-hourbasisandiscalledthebiologicalclock.
Thebodyclockprogrammesustobesleepytwiceaday,between3-5amandagainbetween3-5pm.Afternoonteaandnapareallculturalresponsestoournaturalbiologicalsleepinessintheafternoon.
Oneofthemajorcausesofthetravellers’maladyknownasjetlagisthenon-alignmentofaperson’sinternalbodyclockwithclocksintheexternalworld.Crossingdifferenttimezonesconfusesthebiologicalclock,whichthenhastoadjusttothenewtimeandpatternsoflightandactivity.Tomakemattersmorecomplex,notallinternalbodyfunctionsadjustatthesamerate.Soyoursleep/wakemayadjusttoanewtimezoneatonerate,whileyourtemperatureadjustsatadifferentpace.Yourdigestionmaybeonadifferentschedulealtogether.
Thoughweliveina24－hourday,thenaturaltendencyofthebodyclockistoextendourdaybeyond24hours.Itiscontrarytoourbiologicalprogrammingto‘shrink’ourday.
Thatiswhytravelinginawestwarddirectionismorebody-clockfriendlythanflyingeast.NASAstudiesoflonghaulpilotsshowed that westward travel was associated with significantly better sleep quantity and quality than eastward flights.
When flying west, you are 'extending your day, thus traveling in the natural direction of your internal clock. Flying eastward will involve 'shrinking' or reducing your day and is in direct opposition to your internal clock's natural tendency.
One of the more common complaints of travelers is that their sleep becomes disrupted. There are many reasons for this: changing time zones and schedules, changing light and activity levels, trying to sleep when your body clock is programmed to be awake, disruption of the internal biological clock and working longer hours.
It is often suggested that you adjust your watch as soon as you board a plane, supposedly to try to help you adjust to your destination's schedule as soon as you arrive. But it can take the body clock several days to several weeks to fully adjust to a new time zone.
So, our body clock truly can 'govern' us.
The role of the body clock is to
A．enable us to sleep 6 hours a day.
B．help us adapt to a 24-hour cycle.
C．regulate the body's functions.
D．interfere with the body's functions.
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