What conditions are necessary in order to use the t test for testing the difference between two population Choose the correct answer below O A The population standard deviations are unknown The populations are normally distributed or each sample size is at least 30 OB The population standard deviations are known The samples are randomly selected and independent The populations are normally distributed or each sample size is at least 30 OC The population standard deviations are unknown The samples are randomly selected and independent The populations are normally distributed or each sample size is at least 30 OD The population standard deviations are unknown The samples are randomly selected and independent