"ecstasy" was a popular drug in the 1990s. it produced a sense of euphoria derisively called the "yuppie high." one investigator made a careful sample survey to estimate the prevalence of drug use at stanford university. two assistants were stationed on the main campus plaza and instructed to interview all students who passed through at specified times. as it turned out, 39% of 369 students interviewed said they had used ecstasy at least once. does the investigator’s procedure give a probability sample of stanford students? answer yes or no, and explain.