Answer: A&C is a good choice ,B and C would not be a good choice
Step-by-step explanation:A&C is a good choice because to determine the most popular, you will need to which flavour the students currently buying favours the most and how popular it really is among the students that even those who don't buy it have heard of the flavour and wish to buy
B and C would not be a good choice because the opinions will be biased and result not well concluded because not all students where considered and those whose opinion really count