(1) When someone does something nice for you, you probably want to pay that person back. (2) But some people choose to do something different. (3) They’re paying it forward! (4) In the process they hope to become part of a chain of good deeds that will grow and grow.
Derrick wants to further develop the central idea of this paper by adding a detail after sentence 3. Which of these sentences could BEST follow and support sentence 3?