Which of the Following Situations Is Descriptive of the Existence

Which of the following situations is descriptive of the existence of a negative externality.

A) Vernon studies for his biology test late into the night and oversleeps the next morning, thus missing the test.
B) Nancy is in the library looking for a book.She is talking to herself and consequently disturbs a few people in the library.
C) Bob learns later that he could have purchased a pair of shoes for less than he paid.
D) Jackie has had the flu and has stayed in bed for a week.
E) none of the above