Your Advisor Has Asked You to Reduce the Margin of Error

Your advisor has asked you to reduce the margin of error on your confidence interval from ±5 mg/l to ±1 mg/l. The population standard deviation is known to be 8 mg/. What should you do?

A) Increase the sample size to decrease the margin of error.
B) Decrease the confidence level, C, so that the margin of error will cover a narrower range.
C) Neither A nor B, because you need to decrease the sample size and increase the confidence level.
D) Both A and B, because both will help decrease the margin of error.