Which of the Following Statements Are True?
A) the Pooled-Variances $\geq$

Which of the following statements are true?

A) The pooled-variances t-test is used whenever the population standard deviations are assumed to be equal regardless of the sample size.
B) The unequal-variances t-test is used whenever the population standard deviations are unknown and cannot be assumed to be equal.
C) The z-test can be used as a close approximation to the unequal-variances t-test when the population standard deviations are not assumed to be equal,but samples are large (each n $\geq$ 30) .
D) All of these statements are true.
E) None of these statements is true.