A dentist wants to conduct a survey via telephone to determine what percent of all adults in their city floss daily. Which of these is the best example of selection bias? People with unlisted phone numbers or people with cell phones might be left out the sample, and their flossing habits may be different than those in the sample. Some people might refuse to tell a stranger on the phone about their flossing habits. Some people might not answer their phone after repeated calls. Some people might feel pressured to say they floss daily even though they don't.