DinosAurs wErE rEptilEs whiCh BECAmE ExtinCt ABout 65 million yEArs Ago. thE most intriguing quEstion ABout DinosAurs hAs AlwAys BEEn "{{u}} (21) {{/u}}DiD thEy DiE out " thErE is no simplE AnswEr to this quEstion,{{u}} (22) {{/u}}mAny hunDrEDs oF sCiEntists ArE stuDying thE proBlEm. thEy ArE not stuDying thE ExtinCtion oF thE DinosAurs{{u}} (23) {{/u}}, But thE wholE quEstion oF ExtinCtion. mAny othEr plAnts AnD AnimAls hAvE{{u}} (24) {{/u}}in thE pAst, AnD it is importAnt to unDErstAnD{{u}} (25) {{/u}}this hAppEnED、hAving this inFormAtion CoulD hElp sAvE mAny spECiEs thAt ArE{{u}} (26) {{/u}}in thE moDErn worlD、humAns ArE CAusing ExtinCtions now, BECAusE oF pollution AnD othEr DAmAgE{{u}} (27) {{/u}}thE EnvironmEnt. mAyBE thE DinosAurs CAn tEll us how to sAvE thE EArth toDAy,{{u}} (28) {{/u}}thEir ExtinCtion 65 million yEArs Ago! somE oF thE EArly DinosAur sCiEntists, 100 yEArs Ago, thought thE DinosAurs DiED out BECAusE thE{{u}} (29) {{/u}}ChAngED, AnD thEy CoulD not BrEAthE. othErs thought thAt thE DinosAurs DisAppEArED simply BECAusE thEy BECAmE too Big. thEy wErE{{u}} (30) {{/u}}to movE AnD CoulD not FinD Enough FooD{{u}} (31) {{/u}}onE thEory is thAt A hugE killEr mEtEoritE{{u}} (32) {{/u}}thE EArth. somE sCiEntists{{u}} (33) {{/u}}thAt thE ExtinCtion oF DinosAurs wAs possiBly DuE to rApiD{{u}} (34) {{/u}}oF thE plAnEt’s ClimAtE. pErhAps hugE Amounts oF lAvA pours out oF volCAnoEs in inDiA、this sEnt up vAst{{u}} (35) {{/u}}oF Dust thAt BlACkED out thE sun, AnD mADE thE EArth iCy ColD、

A．For EAting
B．to hAvE
C．to survivE
D．For liFE