Researchers collect samples of fish at a single location of interest in the northern part of the lake. They randomly select 10 fish that weigh less than 1 pound, 10 that weigh between 1 and 2 pounds, 10 that weigh between 2 and 3 pounds, and 10 fish that weigh more than 3 pounds. The amount of PCBs are measured and recorded along with the weight of each fish (mg/lb).

The sampling method used in the PCB study is: (A) simple random sampling because random fish float to the surface. (B) stratified sampling because the fish are stratified by weight in the sampling process. (C) systematic sampling because the researchers systematically chose striped bass to measure PCB contamination. (D) cluster sampling because the location is a cluster.