下列说法正确的是（） ①原命题为真，它的否命题为假 ②原命_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题选择题

下列说法正确的是（　　）

①原命题为真，它的否命题为假

②原命题为真，它的逆命题不一定为真

③一个命题的逆命题为真，它的否命题一定为真

④一个命题的逆否命题为真，它的否命题一定为真．

A．①②

B．②③

C．③④

D．②③④

答案

①原命题为真，它的否命题和原命题没有直接的关系，∴①不正确．

②原命题为真，它的逆命题不一定为真，∴②正确．

③∵逆命题和否命题互为逆否命题，∴一个命题的逆命题为真，它的否命题一定为真，∴③正确．

④一个命题的逆否命题为真，它原命题为真，它的否命题不一定为真．∴④错误．

故选：B．

句型转换

句型转换

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名词解释

刀功