Doctors are researching a new cholesterol medication for teenagers. Eighteen (18) randomly selected male teenagers have taken the new medication long enough for their cholesterol levels to stabilize. Their data follow a normal distribution. The population standard deviation is =30{"version":"1.1","math":"\sigma = 30"}. A confidence interval for which of the following would be most appropriate for estimating the true mean cholesterol level of male teenagers that take the new medication?

Question 4 options:

a) {"version":"1.1","math":"\mu"}, when{"version":"1.1","math":"\sigma"} is known.

b) {"version":"1.1","math":"\mu"}, when{"version":"1.1","math":"\sigma"} is unknown.

c) The true mean of the differences, for paired data.

d) The difference between two means, using independent samples