【单选题】
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①
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②
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③
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④
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【单选题】
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①
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②
<imgsrc="http://121.251.253.213/doc/a@60A71C811B81029FBF602DFB3E611403.png/download?time=636002474654194116&token=D3D19601DFC12A813BAA15BE2BFEF530&filename=png"data-url="doc/a@60A71C811B81029FBF602DFB3E611403.png"data-preview_url_ueditor="doc/a@60A71C811B81029FBF602DFB3E611403.png"/>
③
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④
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【单选题】
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①
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②
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③
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④
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【单选题】
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①
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②
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③
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④
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【单选题】
利用二元关系R的关系图求其对称闭包时,()
②
若两个结点间有一条单向边,则添加一条与其方向相反的边
④
若两个结点间没有边相连,则加上两条方向相反的边
【单选题】
<imgsrc="http://121.251.253.213/doc/a@62CCC9248E6C5CEC9ECB487FFBC2C519.png/download?time=636002476138068722&token=141D02AA787A7554363662D240011921&filename=png"data-url="doc/a@62CCC9248E6C5CEC9ECB487FFBC2C519.png"data-preview_url_ueditor="doc/a@62CCC9248E6C5CEC9ECB487FFBC2C519.png"/>
①
<imgsrc="http://121.251.253.213/doc/a@145B3AC53465C70D90DE0185C036A490.png/download?time=636002476212168852&token=AEBC4369C96DE92EF1B20DF70052F9C3&filename=png"data-url="doc/a@145B3AC53465C70D90DE0185C036A490.png"data-preview_url_ueditor="doc/a@145B3AC53465C70D90DE0185C036A490.png"/>
②
<imgsrc="http://121.251.253.213/doc/a@DBF4517EDFBD9FBFD42E1AEFD412897C.png/download?time=636002476292508993&token=DD1511B0D3AE73B8F5BF2C869A8F52F5&filename=png"data-url="doc/a@DBF4517EDFBD9FBFD42E1AEFD412897C.png"data-preview_url_ueditor="doc/a@DBF4517EDFBD9FBFD42E1AEFD412897C.png"/>
③
<imgsrc="http://121.251.253.213/doc/a@FD0B6F2E4606304A52FAF334BB5BC8E9.png/download?time=636002476370665131&token=D503206A410A9A758039EA014BC6A48F&filename=png"data-url="doc/a@FD0B6F2E4606304A52FAF334BB5BC8E9.png"data-preview_url_ueditor="doc/a@FD0B6F2E4606304A52FAF334BB5BC8E9.png"/>
④
<imgsrc="http://121.251.253.213/doc/a@1AAC94D22983B7C08A700950B6103C74.png/download?time=636002476446481264&token=7B31FF13B112C110C09DD7C42D18DC68&filename=png"data-url="doc/a@1AAC94D22983B7C08A700950B6103C74.png"data-preview_url_ueditor="doc/a@1AAC94D22983B7C08A700950B6103C74.png"/>
【单选题】
Q为有理数集,Q上定义运算*为a*b=a+b-ab,则<Q,*>的幺元为()