Many large cities have considered or passed proposals that ban the use of plastic grocery bags in stores. A concerned student would like to measure if residents of her hometown would consider a similar ban on plastic bags. Standing in a busy shopping area, the student approaches adults and asks, "Items made of plastics are a dangerous, growing source of pollution to our world’s oceans and threaten many animal species. Given this, would you support a ban on plastic shopping bags in our city stores?” How might the results of this survey be biased in estimating the proportion of all town residents who would support a ban on plastic bags?