Chris is the president of an environmental club at his school. To advertise, he posts flyers around the campus that ask "Want to save the environment? Make your voice heard Wednesdays at lunch in room 502." At the next meeting, he polls those in attendance and finds that 80% of students want to ban the sale of plastic water bottles on campus. What type of sample did Chris obtain? Explain why this sampling method is biased. Is 80% likely to be greater than or less than the percent of all students at Chris's high school who want to ban the sale of plastic water bottles on campus? Explain how Chris could avoid the bias described in part (b).