Foraclearerpictureofwhatthestudentknows,mostof 1．______<br/>teachersuseanotherkindofexaminationinadditiontoobjectives<br/>tests.Theyuse“essay”tests,whichrequirestudentstowritelong<br/>answersofbroad,generalquestions.Oneadvantageoftheessay2．______<br/>testisthatitreducestheelementoflucky.Thestudentscannotget 3．______<br/>highscorejustbymakingaluckyguess.Otheradvantageisthatit4．______<br/>showstheexaminermoreaboutthestudent’sabilitytoputfacts<br/>togetherintoameaningfulwhole.Itshouldshowhowdeeplyhe5．______<br/>hasthoughtofthesubject.Sometimes,though,essaytestshave<br/>disadvantages,either.Somestudentsareabletowritegood6．______<br/>answerswithoutreallyknowingmuchaboutthesubject,asother7．______<br/>studentswhoactuallyknowthematerialhavetroubletoexpress 8．______<br/>theirideasinessayform.<br/>Besides,onanessaytestthestudent’sscoremaydependon<br/>theexaminer’sfeelingsatthetimeofreadingtheanswer.Ifheis<br/>feelingtiredorbored,thestudentmayreceivealowerscorethan<br/>heshould.Anotherexaminerreadingthesameanswermightgiveit<br/>muchhighmark.Fromthisstandpointtheobjectivetestgiveseach9．______<br/>studentafairerchance.<br/>Whenanobjectivetestoranessaytestareused,problems10．______<br/>arise.Whensomeobjectivequestionsareusedalongwithsome<br/>essayquestions,however,afairlyclearpictureofthestudent’s<br/>knowledgecanusuallybeobtained.

20A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、120、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、130、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、A、B、C、D、140、A、B、C、D、A

以下集合A={a,b,c,d}上关系，其中（ ）是等价关系。 A: {(a,a),(a,d),(b,b),(b,c),(c,b),(c,c),(d,a) } B: {(a,a),(a,b),(b,a),(b,b),(c,c),(c,d),(d,c),(d,d)} C: {(a,a),(b,b),(b,c),(c,b),(c,c),(d,a),(d,d)} D: {(a,a),(a,b),(b,a),(b,b),(b,c),(c,b),(c,c),(d,d)}

设A={a,b,c,{a,c}},B={a,c,d},则B-A=____,A⊕B=____。 A: {a,c,d}, {{a,c},b,d} B: {d}, {a,c,b,d} C: {d}, {{a,c},b,d} D: {d}, {a,c}

A: A＞B＞C＞D B: D＞C＞B＞A C: D＞B＞A＞C D: C＞A＞B＞D