A newborn baby has extremely low birth weight (ELBW) if it weighs less than 1000 grams. A study of the health of such children in later years examined a random sample of 219 children. Their mean weight at birth was \bar {x} = 810 grams. This sample mean is an unbiased estimator of the mean weight \mu in the population of all ELBW babies. This means that
A. the average sample mean \bar {x}, over all possible samples, is equal to \mu.
B. the sample mean \bar {x} is always equal to \mu.
C. the sample mean \bar {x} will have a distribution that is close to Normal.
D. None of the above.
