Which of the Following People Are Practicing Serial Monogamy

Which of the following people are practicing serial monogamy?

A) Ainsley, who marries her high school sweetheart and remains faithful for a lifetime.
B) Leo, who dates multiple people at a time until committing to one relationship.
C) Antonio, who dates several different people over time, but stays sexually exclusive during each relationship.
D) Sofia, who avoids hookup culture until graduating from college.
E) Liam, who maintains a long-standing affair with one other person after getting married.