You and a Friend Were in Line for a Movie

Multiple Choice

You and a friend were in line for a movie when you noticed the woman in front of you sneezing and coughing. Both of you were equally exposed to the woman's virus, but over the next few days, only your friend acquired flu-like symptoms and was ill for almost a week before recovering. Which one of the following is a logical explanation for this?

A) Your friend had antibodies to that virus.
B) You had an immunological memory of that virus.
C) Your friend had an autoimmune disorder.
D) Your friend had allergies.