Which of the following best describes an example of normative social influence?

Which of the following best describes an example of normative social influence?
 
  a. Carrie is studying with a group of friends. When comparing answers on the practice test, she discovers that they all answered the question differently than she had. Instead of speaking up and telling them she thinks the answer is something else, she agrees with their answer because she figures they must be right.
  b. Samantha is supposed to bring a bottle of wine to a dinner party she is attending. She doesn't drink wine herself but figures she can just ask the store clerk for advice on what kind to buy.
  c. Miranda is out to lunch with her boss and coworkers. Her boss tells a joke that makes fun of a certain ethnic group, and everyone else laughs. Miranda doesn't think the joke is funny but laughs anyway.
  d. Charlotte is flying on an airplane for the first time. She is worried when she hears the engine make a strange noise but feels better after she looks at the flight attendants and sees that they are not alarmed.