What is the potential source of bias in this question

Question

An opinion poll calls 2000 randomly chosen residential telephone numbers then asked to speak with an adult member of the household the interviewer asks box office revenues are at an all-time high how many movies have you watched any theater in the past 12 months and all 1131 people responded the researchers use the responses to estimate the main number of movies adults have watched any movie theater in the past 12 months.What is the potential source of bias in this question

Answer 1

The assumption is that all adults have a residential phone number.  They may not.