One major reason that the two-sample t procedures are widely used is that they are quite robust. This means that
(a) t procedures do not require that we know the standard deviations of the populations.
(b) t procedures work even when the Random,
Normal, and Independent conditions are violated.
© t procedures compare population means,
a comparison that answers many practical questions.
(d) confidence levels and P-values from the t
procedures are quite accurate even if the population distribution is not exactly Normal.
(e) confidence levels and P-values from the t procedures are quite accurate even if outliers and strong skewness are present
Choice D, the general rule is that t is ok to use with skew when n > 30