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下列说法: 1若一个命题的否命题是真命题,则这个命题不一定是真命题;2若一个命题的逆否命题是真命题,则这个命题是真命题;3若一个命题的逆命题是真命题,则这个命题不一定是真命题;4若一个命题的逆命题和否命题都是真命题,则这个命题一定是真命题;其中正确的说法是( )A.
①②
B.
①③④
C.
②③④
D.
①②③
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