If the Width of a Confidence Interval For $\mu$ Is Too Wide When the Population Standard Deviation

Multiple Choice

If the width of a confidence interval for $\mu$ is too wide when the population standard deviation $\sigma$ is known, which one of the following is the best action to reduce the interval width?

A) Increase the confidence level
B) Reduce the population standard deviation $\sigma$
C) Increase the population mean $\mu$
D) Increase the sample size n
E) None of the above answers are correct.