Which of the following statements is correct?

a. Whenever a simple random sample is selected and the value of the sample mean is used to estimate the value of the sampled population mean, we can expect the sampled population mean to exactly equal the sample mean.

b. E(x with bar on top) = , where is the sampled population mean.

c. Only when the sampled population has a normal distribution, is the sampling distribution of x with bar on top normally distributed.

d. All of the above.