Rob sent an email survey to 2,000 cell phone owners asking about their satisfaction with their current plan. Only 256 people returned the survey and they were predominately 18-24 years old. Which of the following statements is true?

Rob is ignoring the assumption that all survey participants will want to act independently.

The survey likely has bias because the people who could not answer differ from those who did answer.

Rob included too many people on the survey list, affecting the data collected.

The survey suffers from census issues because only 256 people responded.