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NO.PZ2023061301000027 问题如下 Whiof the following statements is correregarng the chi-square test ofinpennce? A.The test ha one-sirejection region. B.The null hypothesis is ththe two groups are pennt. C.If there are two categories, eawith three levels or groups, there are sixgrees of freem. A is correct. The test statistic inclus squarefferences between the observenexpectevalues, so the test involves only one si, the right si. B is incorrectbecause the null hypothesis is ththe groups are inpennt, anC isincorrebecause with three levels of groups for the two categoricvariables,there are four grees of freem. 我知道公式 =（r-1)(C-1), 可是根据题目， 不是2个categories， 每个categeires 有3个子类目， 所以 row 是2， column 是3吗， 所以算出来是2吗， 为什么解析中说是一个三行三列的表格呢， 谢谢

NO.PZ2023061301000027问题如下 Whiof the following statements is correregarng the chi-square test ofinpennce? A.The test ha one-sirejection region.B.The null hypothesis is ththe two groups are pennt.C.If there are two categories, eawith three levels or groups, there are sixgrees of freem. A is correct. The test statistic inclus squarefferences between the observenexpectevalues, so the test involves only one si, the right si. B is incorrectbecause the null hypothesis is ththe groups are inpennt, anC isincorrebecause with three levels of groups for the two categoricvariables,there are four grees of freem. 请问老师，b错在哪里呀？