Answer:b. informational social influence
Explanation: When we don't know what to do but we believe that someone else has a valid knowledge on that subject , then we use their information to decide what to do , or conform to their behavior because we believe this other person knows what we don't know this is infomational social influence.
For example if you landed from a flight in a place you don't know, it is very likely that you will follow other passengers because you assume they know where they are going and following them is likely to take you where everyone picks up their baggage.
Informational social influence refers to Changing our opinions or behavior so that we can conform to what we believe to be an accurate information.
Libby is doing the same thing she listens to everyone else so that she can learn how to address the professor , because she believes the other students knows .