光纤有哪些主要特性和参数？
光纤的特性和参数可概括如下：
（ 1）传输特性：包括损耗、色散；
（ 2） 光学特性： 包括折射率分布、 数值孔径、 截止波长、 模长直径。
（3）几何特性：包括芯径、包层外径、同芯度误差、包层不圆度。
（4）机械特性
（ 5）温度特性
暂无解析
Tammy:Someoneisatthedoctor.
Richard:______.
Hepaidtheboy$10forwashingtenwindows,mostof____hadn'tbeencleanedforatleastayear.
Inasecond-handbookshop,Billycameacrossabookwhichhethoughtwascertainlya____edition.
"Lookwhatyou'vedone!You______morecareful."
Passage3
Questions11to15arebasedonthefollowingpassage:
“...WearenotabouttoentertheInformationAgebutinsteadareratherwellintoit.”Presentpredictionsarethatby1990,aboutthirtymillionjobsintheUnitedStates,oraboutthirtypercentofthejobmarket,willbecomputer-related.In1980,onlytwenty-onepercentofallUnitedStateshighschoolsownedoneormorecomputersforstudentuse.(79)Inthefallof1985,anewsurveyrevealedthathalfofUnitedStatessecondaryschoolshavefifteenormorecomputersforstudentuse.Andnoweducationalexperts,administrators,andeventhegeneralpublicaredemandingthatallstudentsbecome“computerliterate(慢点…的).”“Bytheyear2000knowledgeofcomputerswillbenecessaryinovereightypercentofalloccupations.Soonthosepeoplenoteducatedincomputerusewillbecomparedtothosewhoareprintilliteratetoday.”
Whatis“computerliteracy”?Thetermitselfseemstoimplysoonextentof“knowing”aboutcomputers,butknowingwhat.Thecurrentopinionseemstobethatthisshouldincludeageneralknowledgeofwhatcomputersare,plusalittleoftheirhistoryandsomethingofhowtheyoperate.
Therefore,itisvitalthateducatorseverywheretakeacarefullooknotonlyatwhatisbeingdone,butalsoatwhatshouldbedoneinthefieldofcomputereducation.Todaymostadultsarecapableofutilisingamotorvehiclewithouttheslightestknowledgeofhowtheinternal-combustionengineworks.Weeffectivelyusealltypesofelectricalequipmentwithoutbeingabletotelltheirhistoriesortoexplainhowtheywork.(80)Businesspeopleforyearshavemadegooduseoftypewritersandaddingmachines,yetfewhaveeverknownhowtorepairthem.Why,then,attempttoteachcomputersbyteachinghoworwhytheywork?
Rather,wefirstmustconcentrateonteachingtheeffectiveuseofthecomputerasthetoolis.
“Knowinghowtouseacomputeriswhat’sgoingtobeimportant,wedon’ttalkabout‘automobileliteracy.‘Wejustgetinourcarsanddrivethem.”
11.In1990,thenumberofjobshavingnothingtodowithcomputersintheUnitedStateswillbereducedto________.
A)79millionB)30millionC)70millionD)100million(C)
12.Theexpression“Printilliterate”(Para.1,Line16)refersto________.
A)onewhohasneverlearntprintingB)onewhoisnotcomputerliterate
C)onewhohasneverlearnttoreadD)onewhoisnotabletouseatypewriter(C)
13.Thefirstparagraphismainlyabout________.
A)recentpredictionsofcomputer-relatedjobsB)thewideuseofcomputersinschools
C)theurgencyofcomputereducationD)publicinterestincomputers(C)
14.Accordingtotheauthor,theeffectivewaytospreadtheuseofcomputersistoteach____.
A)whatcomputersareB)howtousecomputers
C)wherecomputerscanbeusedD)howcomputerswork(B)
15.WhichofthefollowingstatementsisFALSE?
A)Whattoteachaboutcomputersshouldbereconsidered.
B)Thosewhoarenoteducatedincomputerusewillfinditdifficulttogetajob.
C)HumansocietyhasalreadyenteredtheInformationAge.
D)Thosewhowanttousecomputersshouldknowhowcomputersoperate.
