A batch consists of 10 equal-sized boxes of lightbulbs.

The correct answer is A. stratified sampling . In the CSSBB-aligned sampling material, stratified sampling is defined as dividing the population into subgroups, or strata , based on a common characteristic and then taking a sample from each subgroup . The source gives examples such as selecting units from each shift, machine, or pallet, which is the same logic used here with one bulb being chosen from each box.

This differs from cluster sampling , where one cluster is selected and then the entire cluster is evaluated. The same source explains that in cluster sampling, the sampling occurs in the choice of the cluster, and the chosen cluster itself is then 100% analyzed . That is not what is happening in this question, because the team is not selecting one entire box and checking all bulbs in it. Instead, they are taking one item from each of several defined groups. That is the textbook definition of stratified sampling. Therefore, the verified CSSBB-based answer is A. stratified sampling .