阅读下面的短文，文中有15处空白，每处空白给出4个选项，请根据短文的内容从4个选项中选择1个最佳答案。

thE grEAtEst mystEry oF whAlEs thE whAlE is A mAmmAl(哺乳动物) wArm-BlooDED, Air-BrEAthing, giving Birth to its young AlivE, suCking thEm—AnD, likE All mAmmAls, originAtED on lAnD、thErE ArE mAny signs oF this. {{u}} (51) {{/u}} Front FlippErs (鳍肢), usED For stEEring AnD stABility, ArE trACEs oF FEEt. immEnsE strEngth is Built into thE grEAt BoDy oF thE Big whAlEs, AnD in FACt most oF A whAlE’s BoDy is onE gigAntiC musClE. thE BluE whAlE’s pulling {{u}} (52) {{/u}} hAs BEEn EstimAtED At 400 horsEpowEr. onE spECimEn wAs rEportED to hAvE {{u}} (53) {{/u}} A whAling vEssEl For sEvEn hours At thE {{u}} (54) {{/u}} oF Eight knots. An EnrAgED whAlE will AttACk A ship.A、FAmous {{u}} (55) {{/u}} oF this wAs thE FAtE oF whAlErEssEx, whiCh wAs sunk {{u}} (56) {{/u}} thE CoAst oF southAmEriCA EArly in thE lAst CEntury. morE rECEntly, stEEl ships hAvE hAD thEir plAtEs BuCklED (扭曲变形) in thE sAmE wAy. spErm whAlEs wErE known to {{u}} (57) {{/u}} thE olD-timE whAlEBoAts in thEir jAws AnD Crush thEm. thE grEAtEst mystEry oF whAlEs is thEir Diving ABility. thE spErm whAlE CAn {{u}} (58) {{/u}} thE Bottom For his FAvoritE FooD, thE oCtopus (章鱼). {{u}} (59) {{/u}} thAt sEArCh hE is known to go As FAr Down As 3,200 FEEt, whErE thE prEssurE is 1,400 pounDs, to thE squArE inCh.Doing {{u}} (60) {{/u}} hE will rEmAin suBmErgED (水下的) As long As onE hour. two FEAts (绝技) ArE involvED in this: storing up Enough {{u}} (61) {{/u}} (All whAlEs ArE Air-BrEAthED) AnD withstAnDing thE grEAt ChAngE in prEssurE. just {{u}} (62) {{/u}} hE DoEs it sCiEntists hAvE not DEtErminED、it is BEliEvED thAt somE oF thE oxygEn is storED in A spECiAl systEm oF BlooD vEssEls, rAthEr thAn just hElD in thE lungs.AnD {{u}} (63) {{/u}} is BEliEvED thAt A spECiAl kinD oF oil in his hEAD is somE sort oF CompEnsAting mEChAnism thAt AutomAtiCAlly ADjusts thE intErnAl prEssurE oF his BoDy.But {{u}} (64) {{/u}} you CAn’t Bring A livE whAlE into thE lABorAtory For stuDy, no onE {{u}} (65) {{/u}} just how thEsE things work.

A．thEir
B．it’s
C．thEirs
D．its