The falling action in "Romeo and Juliet" typically includes events that follow the climax and lead to the resolution of the story. In this case, the event that is part of the falling action is:
D. Juliet and Friar Lawrence devise a plan to fake her death.
This event occurs after the climax of the play, which is usually considered to be the deaths of Mercutio and Tybalt, leading to Romeo's banishment. The plan to fake Juliet's death sets off a chain of tragic events that ultimately leads to the resolution of the play.