Evaluate the Following Generalization(s), Identifying Sample, Population, Attribute of Interest

Evaluate the following generalization(s), identifying sample, population, attribute of interest, and the extent to which the claims involved are knowable. Consider carefully the size and diversification of the sample and the extent to which the population differs or may differ from the sample; remember, what's important is that the sample be representative.
A poll of fifty weight lifters at a southern California gym determined that thirty-three payed close attention to their diets as well as to their exercise. Of those thirty-three, twenty-five (50 percent of the original fifty) made it a point to eat more than the minimum daily amount of protein for large adults, and twenty (40 percent of the original fifty) took vitamin pills and other dietary supplements. The chain of health-food stores that took the poll concluded that weight lifters constitute a substantial market for its products, since it is likely that 40 percent of all weight lifters across the country take vitamin pills and supplements and that an additional 10 percent are at least highly conscious of their diets.