There may be more than one correct statement , check all that are true .

a) In interval estimation of the population mean , the fundamental difference between the t and z procedures is that we use t for small sample sizes and z for large sample sizes .

b) On average , the sample means equals the population mean .

c)All else being equal , a 99% confidence interval for mu will be wider than the corresponding 95% interval .

d) If the sample size is small , the sampling distribution of the sample mean cannot be normal .