Suppose salary in your firm has a mean of and a known standard deviation of $18,000. What best characterizes the sampling distribution of the sample mean for a sample size of 100?

Select the best answer:

A) The distribution has an unknown standard deviation. B) The distribution is approximately normal with a standard deviation of $18,000. C) The distribution has unknown shape with a standard deviation of $1,800. D) The distribution is approximately normal with a standard deviation of $1,800.

I think the answer is D but not sure- please show caluations