Choice b and choice c are required for an independent random sample.
explanation:
Sample selected randomly from a population is random sample. Independent random samples are samples, collected from two different datas or samples. If one sample has been selected , it has no influence on the selection of another sample.
Even if one or more samples are selected , its probability remains constant for all selections. Independent random sample allows for replacement also.
The disadvantage of such a sample process is, that it can lead often to sampling errors.
The advantage of such sampling method, is that it helps reduce the cost and helps in including important subpopulations.
