When calculating a 95% confidence interval for the difference between two means, which of the following is true?
a) When the confidence interval ranges from a positive value to a positive value, we find that there is conclusive evidence (at 95% confidence) that both population means are positive.
b) When the confidence interval ranges from a negative value to a positive value, we find that there is conclusive evidence (at 95% confidence) that there is a difference between the two population means.
c) When the confidence interval ranges from a negative value to a negative value, we find that there is conclusive evidence (at 95% confidence) that both population means are negative.
d) When the confidence interval ranges from a negative value to a positive value, we find that there is not conclusive evidence (at 95% confidence) that there is a difference between the two population means.