An article entitled "Couch Potato Nation" describes a report by the federal Centers for Disease Control and Prevention that "analyzed responses from 119,000 people who were asked in 1996 about their physical activity during the month prior to the survey."8 Suppose the survey was carried out by telephone, and the researchers had reason to suspect that whoever answers the phone might tend to be the least active household member. To offset this bias, they could ask about the physical activity of all household members. Would this be a convenience sample, a systematic sample, a cluster sample, or a stratified sample?