资料：Whenweseewell，wedonotthinkaboutoureyesveryoften.Itisonlywhenw

资料：Whenweseewell，wedonotthinkaboutoureyesveryoften.Itisonlywhenwecannotseeperfectlythatwerealizehowimportantoureyesare. Peoplewhoarenear-sightedcanonlyseethingsthatareveryclosetotheireyes，Everythingelseseemsblurry(=unclear).Manypeoplewhodoalotofwork，suchaswriting，readingandsewingbecomenear-sighted. Peoplewhoarefar-sightedsufferfromjusttheoppositeproblem.Theycanseethingsthatarefaraway，buttheyhavedifficultyinreadingabookunlesstheyholditatarm’slength.Iftheywanttodomuchreading，theymustgetglasses，too. Otherpeopledonotseeclearlybecausetheireyesarenotexactlytherightshape.Theyhavewhatiscalledastigmatism.This，too，canbecorrectedbyglasses.Somepeople’seyesbecomecloudybecauseofcataracts.Longagothesepeopleoftenbecameblind.Now，however，itispossibletooperateonthecataractsandremovethem. Havingtwogoodeyesisimportantforjudgingdistances.Eacheyeseesthingsfromaslightlydifferentangle.Toprovethistoyourself，lookatanobjectoutofoneeye；Thenlookatthesameobjectoutofyourothereye.Youwillfindtheobject’srelationtothebackgroundandotherthingsaroundithaschanged.Thedifferencebetweenthesetwodifferenteyeviewshelpsustojudgehowfarawayanobjectis.Peoplewhohaveonlyoneeyecannotjudgedistanceaspeoplewithtwoeyes. Havingtwoeyesinsteadofoneisparticularlyusefulfor______.

A.looking over a wide area

B.seeing objects far away

C.judging distances

D.seeing at night

正确答案是C