Idoent understand what a metonymy is?

Read this excerpt from tim o’brien‘s “ambush” “i had already pulled the pin on a grenade. i had come to a crouch” which literary device is most clearly shown in this excerpt?

What do the excerpts have in common? both point out the tragic nature of situations in which children make journeys without their parents. both describe what immigrant children must do to survive when traveling to the united states. both explain why most children want to leave central america without their parents. both indicate the tragic problems and their consequences that children in central america must face.

Which work would represent a change to the artistic medium of this original work?