To test the effectiveness of a liquid supplement that is supposed to help forgetful people with the memory, 400 college students are recruited for a study and divided into two groups. Group A with 250 students receives the supplement, while group B with 150 students receives some colored water. Neither group is told what they received. After several weeks, they are given a memory test.This study can best be described asthe placebo effecta survey using quota samplinga controlled placebo experimenta censusa survey using simple random sampling