Because 25 percent of the students in my morning statistics class watch eight or more hours of television a week, I conclude that 25 percent of all students at the university watch eight or more hours of television a week. The most important logical weakness of this conclusion would be

Multiple Choice
 
relying on a sample instead of surveying every student.
 
using a sample that may not be representative of all students.
 
failing to correct for unconscious interviewer bias.
 
assuming cause and effect where none exists.