To determine how students at a particular college feel about cigarette smoking in public places, all students in the college who chose to have their email address published in the college directory were sent an email with a link to an online survey. What is wrong with this sampling method?

A. Nothing, since students could go online to give their opinion.
B. Only smokers should have been surveyed.
C. They should have only sent the email to every 5th student in the directory.
D. The sampling method would result in a sample size that is too large.
E. Not all students would have an email listed in the student directory.