In which of the following scenarios can we calculate a confidence interval for the population mean?

Choose all that apply.

a. A random sample of 60 cell phone calls is selected and the mean length of calls is determined to be 3.25 minutes with a standard deviation of 4.2 minutes.
b. A random sample of 15 women athletes is selected and their mean weight is determined to be 136 pounds. Female athlete weights are known to be normally distributed with a population standard deviation of 20 pounds.
c. A random sample of 14 cell phone calls is selected and the mean length of calls is determined to be 3.25 minutes with a standard deviation of 4.2 minutes.
d. A random sample of 35 women athletes is selected and their mean weight is determined to be 136 pounds. Female athlete weights are known to be normally distributed with a population standard deviation of 20 pounds.