Which of the following is not a rule for using the t-test?

a	the sample comes from a normal distribution
b	The data comes from a simple random sample
c	for sample sizes 40 or greater, t-procedures can be used even if data is heavily skewed
d	for sample sizes 15 or greater, t-procedures can be safely used except in the presence of outliers or strong skewness.
e	For sample sizes of 15 or less, t-procedures cannot be used