可以麻烦解释一下b错在哪了吗

NO.PZ2021062201000019 问题如下 Whiof the following statements is correregarng the chi-square test of inpennce? 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 six grees of freem. A is correct. The test statistic comprises squarefferences between the observeanexpectevalues, so the test involves only one si, the right si. B is incorrebecause the null hypothesis is ththe groups are inpennt, anC is incorrebecause with three levels of groups for the two categoricvariables, there are four grees of freem.本题考察关于卡方检验的概念，由于检验统计量包含观测值和预期值之间的平方差，因此检验仅涉及一侧，即右侧，所以选 那自由度应该是（2-1）*（3-1）=2为什么是（3-1）*（3-1）=4？

NO.PZ2021062201000019 问题如下 Whiof the following statements is correregarng the chi-square test of inpennce? 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 six grees of freem. A is correct. The test statistic comprises squarefferences between the observeanexpectevalues, so the test involves only one si, the right si. B is incorrebecause the null hypothesis is ththe groups are inpennt, anC is incorrebecause with three levels of groups for the two categoricvariables, there are four grees of freem.本题考察关于卡方检验的概念，由于检验统计量包含观测值和预期值之间的平方差，因此检验仅涉及一侧，即右侧，所以选 卡方检验不一定是单尾啊，老师的课件中举的例子，P396，第一问不就是个双尾的嘛

NO.PZ2021062201000019问题如下 Whiof the following statements is correregarng the chi-square test of inpennce? 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 six grees of freem. A is correct. The test statistic comprises squarefferences between the observeanexpectevalues, so the test involves only one si, the right si. B is incorrebecause the null hypothesis is ththe groups are inpennt, anC is incorrebecause with three levels of groups for the two categoricvariables, there are four grees of freem.本题考察关于卡方检验的概念，由于检验统计量包含观测值和预期值之间的平方差，因此检验仅涉及一侧，即右侧，所以选卡方分布的线不是一条第一象限positively skewness的线，拒绝域左面和右面都有，只是右面的比较重要，一般都用右面的吗，这题我第一选择就没选A

NO.PZ2021062201000019 The null hypothesis is ththe two groups are pennt. If there are two categories, eawith three levels or groups, there are six grees of freem. A is correct. The test statistic comprises squarefferences between the observeanexpectevalues, so the test involves only one si, the right si. B is incorrebecause the null hypothesis is ththe groups are inpennt, anC is incorrebecause with three levels of groups for the two categoricvariables, there are four grees of freem. 本题考察关于卡方检验的概念，由于检验统计量包含观测值和预期值之间的平方差，因此检验仅涉及一侧，即右侧，所以选请老师一下C以及考点