Haveyouwonderedwhyyouhavetwoeyesandwhytheyaresetclosetogetheronthefrontofyourface?Thereasonsaresimpleandimportant.

Youreyesareliketwosmallcameras.Acameracatchesanimage（影像）ofanobjectandrecordsitonfilm.Similarlywhenyoulookatsomethingeacheyetakesinwhatitseesandsendsthisimagetothebackoftheeyeball.Becauseyoureyesaresetclosetogethertheyseetheworldfromaboutthesameheightbutfromalittledifferentangles(角度).Whileyourrighteyeseesanobjectalittletotherightyourlefteyeseesthesameobjectabittotheleft.Workingasateamtheeyessendtheimagestoyourbrainthenyourbrainputsthemtogetherandyouseeasingleimageinthecentre.

Seeinginstereomeansseeingwithtwoeyesworkingtogetherwhichiscalledstereoscopicsight.Thisallowsyoutoseetheworldin3-D.Seeingdepth（深度）helpsyoutojudgehowfaritisbetweenyouandtheobjectsyouseeandthenadjust（调整)tothechanginganglesothatyoucanseesomethingclearlywhenyoumovecloserorfartheraway.Ifimagesarecomingfromonlyoneeyehoweverheightandwidth（宽度）—canbeperceived.Soifyouseewithoneeyeyouwillgeta2-Dimageasinaphotograph.

Nowconsiderwhyyourtwoeyesareonthefrontofyourface.Thinkofotheranimalsjustlikeyou.Theyareallhunting（猎杀）animalslikelionsandtigers.Thisprovidesafieldofsightabout180degreewidewhichiscalledbinocularsight.Ontheotherhandanimalsthatarehuntedhaveeyesonthesidesoftheheadwhichprovidesnearly360-degreefieldofsight.Howevertheydon’thavestereoscopicsight.Itisdifficultforthemtojudgehowfaradangeris.

Withbothstereoscopicandbinocularsighthumansandhuntinganimalssharetheabilitytoseefromsidetosideandtojudgehowfaritisfromotherobjects.Ifyouthinkitwouldbegreattohaveanotherkindofsightperhapswithhundredsoftinyeyeslikemanyinsects(昆虫)dothinkagain!Eachtinyinsecteyeseesonlyatinypart.Besideswhatifyouneededglasses?Begladfortheeyesightthatyouhave.

1. InParagraph2thewriterwantsto__________.

A.tellushowourtwoeyeswork

B.showtheimportanceofeyes

C.compareoureyeswithcameras

D.suggestusingtwoeyesproperly

2.Theunderlinedword“perceive