Answer:
C. Buy this new hair tonic. It's cool. Everyone's doing it
Step-by-step explanation:
A bandwagon fallacy which is sometimes called "an appeal to common belief" simply means people doing something because other people are doing it.
The option C is an argument which is a bandwagon fallacy because it is appealing to common belief because it is believed that everyone is doing it.
The statement is is trying to get people to buy the new hair tonic because that is what everybody is using.