Which of the following is the best example of dramatic irony?

a. your friend gives a confusing explanation for why he did something and you respond, "that's obvious."
b. a movie in which a man is rude to an older female stranger on the street. you know that woman is, in fact, his mother, although he does not.
c. a cowboy movie set at a rodeo and the person who rides the bucking bronco the longest is an 8-year-old girl in a pink tutu.
d. a television show that stars male and female business partners.