Which of the following is not one of the conditions that must be satisfied in order to perform inference about the slope of a least-squares regression line?

(a) For each value of x, the population of y-values is Normally distributed.

(b) The standard deviation s of the population of y-values corresponding to a particular value of x is always the same, regardless of the specific value of x.

(c) The sample size—that is, the number of paired observations

(x, y)—exceeds 30.

(d) There exists a straight line y = a + bx such that, for each value of x, the mean my of the corresponding population of y-values lies on that straight line.

(e) The data come from a random sample or a randomized experiment.