Answer: the correct answer is A. Having an unbiased estimator means that the mean of the means of all possible samples of the same size would be the same as the population mean.
Step-by-step explanation:
The problem is that is just one sample of 23 bats so the experiment is very limited to say that the population mean is 503.4 since an unbiased estimator is in more mathematical terms if the estimator (i.e. the sample mean) equals the parameter (i.e. the population mean), then it's an unbiased estimator.