What Does It Mean to Say That the Sample Mean

Multiple Choice

What does it mean to say that the sample mean is an unbiased estimator of the population mean?

A) The sample means will vary minimally from the population mean.
B) The sampling distribution of possible sample means is approximately normally distributed,regardless of the shape of the distribution in the population.
C) If we select a sample at random,then on average we can expect the sample mean to equal the population mean.
D) all of the above