Analysis: Analyze the * * * similarity of three samples. Among the three kinds of sampling, simple random sampling is selected one by one from the population, systematic sampling is divided into several parts in advance according to certain rules, and stratified sampling is divided into several layers, and then selected accordingly.
Answer: According to sampling, the population is divided into disjoint layers, and then a certain number of individuals are independently extracted from each layer according to a certain proportion, and the individuals extracted from each layer are combined as samples. This sampling method is called stratified sampling.
According to the significance of stratified sampling, c is correct,
So choose C.
Comments: Which sampling form to choose for sampling depends on the overall situation given by the topic. If the overall number of people is small, lottery can be used; If the total number is large and there is no difference in individual parts, systematic sampling can be used; If the individual difference of the population is large, stratified sampling can be used.