Which of the following statements about the chi-squared test of independence is true? Seleccione una: O a. The null hypothesis is Ho : X2 = 0, where X2 is the test statistic calculated from the sample data. O b. For testing independence in a contingency table with r rows and c columns, the reference chi-squared distribution has r x c degrees of freedom. O c. It is used to test for independence between two quantitative variables. O d. Interchanging two rows in a contingency table has no effect on the value of the chi-squared test statistic