Sally Wants to Know What Percentage of Canadian University Students

Sally wants to know what percentage of Canadian university students are receiving financial aid their first year in university. Sally attends a small university with a large percentage of students who commute to campus every day. Sally stands outside of the residence dining hall one weekday evening and hands out surveys to every third person entering the hall for dinner. Sally's data will be invalid because _.

A) she did not use random sampling
B) she did not define her population
C) she did not do a pilot test of her survey
D) she did not use a representative sample