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. Weshouldtakegoodcareofoureyes______.
A.even if we can see well B.only when we cannot see perfectly C.only when we realize how important our eyes are D.only when we can see well正确答案A
