Under which conditions can z-tests be used instead of t-tests for population means?
I. If σ is known, and sample comes from a normal distribution.
II. If σ is unknown, and the sample comes from a normal distribution
III. If σ is known, and the sample size is less than 30.
__A) Only I
__B) Only I and II
_ C) Only I and III
__D) Only II and III