Jungerscomparedthehipandlegjointsofapes.Henotedthatinhumanbeingsthesejointsareexceptionallylargerelativetobodysize.Thisisbecausetheybearallofthebody’sweightwhenapersonisstanding.Inapes，however，thelegandhipjointsaresmallerbecauseapesalsousetheirforelimbsforsupport.
JungersthenexaminedthehipandlegjointsofanaustralopithecineskeletonnicknamedLucyandfoundthatitsjointsdisplaybothhumanlikeandapelikecharacteristics，JungersconcludedthatLucy’sphysicaldevelopment-aswellasthatofother　australopitheciness-fallssomewherebetweenhumanbeingsandapes.Whileaustralopithecinesmayhavewalkedinanuprightmanner，theirgaitwasprobablyfardifferentfromtheuprightmovementexhibitedbymodernhumanbeings.

Jungers’findingshowedthat_____.
A．humanbeingswalkeduprightlaterthanaustralopithecines
B．bipedalismmighthavedevelopedsuddenlyinearlyhumans
C．earlyhumansmighthavelearnedtowalkgradnally
D．humanbeingsevolvedfromaustralopithecinesratherthanfromapes


Jungers’reportwasbaseduponhiscomparisonof_____.
A．thebodysizeofpeople,apesandaustralopithecines
B．theskeletonofpeople,apesandaustralopithecines
C．thehipsandlegjointsofpeople,apesandaustralopithecines
D．thesizeofhipandlegjointsofmodernpeopleandaustralopithecines


WhichofthefollowingisTRUEaboutLucyaccordingtoJunger?
A．Lucywalkedmorelikeapesthanlikehumanbeings.
B．Lucymovedherstepsinthesamemanneraspeople.
C．Lucymightwalkquitedifferentlyfrommodernman.
D．Lucyhadhipandlegjointslikepeople’s.


Whyisthesizeofthehipandlegjointsimortantinestablishingthehumanhabitofbipedalism?
A．theysupporthumanbodyinanuprightposition.
B．theyaretheonlyobservableevidenceinaustralopithecinesstudy.
C．theevolutionofthejointsisthefastestinanimals.
D．theymarkthemajordifferencebetweenhumansandhumanlikeanimals.
Passage3
Mountingevidencehasledastronomerstojustsuchanimprobableconclusion：Atleast90percentandpossibly99percentofallmatterintheuniverseiscompletelyinvisible.Astronomerscallthisinvisiblestuffdarkmatter.
Anastronomerfirstreportedtheinvisiblematterafternotingsomeunusualbehaviourinvisiblematter.In1933，SwissastrophysicistFritzZwickyobservedthatgalaxies（星系）inaclusterofgalaxiestravelledathigherspeedsthanexpected.Heconcludedthatsomethingwascausingstrangegravitationaleffectsonthesegalaxies.
Galaxiesarelikevastislandsindeepspacecontainingbillionsofstarsthatareheldtogetherbytheforceofgravity.Somegalaxiesarepartoflargersystemscalledclusters，whichcontainmanygalaxies.Mostgalaxies，however，belongtosmallersystemscalledgroups.Groupsandclustersinturnformevenlargerstructuresknownassuperclusters.Justastheforceofgravitykeepsstarstogetheringalaxies，sotheforceofgravityappearstokeepgalaxiestogetherinclusters.
Thissameforceofgravitykeepsplanetsorbitingaroundthesun，ratherthanflyingoffintospace.Howgreataforcegravityexertsdependsonthemassoftheobjectsattractedandthedistancebetweenthem，aprinciplediscoveredbyNewton.Theamountofmassandthedistancebetweenobjectsalsodeterminehowfasttheobjectstravelastheyorbiteachother.Forexample，inoursolarsystem，thesunisthemostmassiveobject，makingupabout99．9percentofthemassofthesolarsystem，andtheforceofitsgravitykeepsEarthandtheotherplanetsinorbitaroundit.Theorbitalspeedsoftheplanetsdeclinewithincreasingdistancefromthesun.Theplanetnearesttothesun，Mercury，travelsatanorbitalspeedof48kilometerspersecond，whilethedistantplanetPlutoorbitsatspeedof4．7kilometerspersecond.