Enrique’s head throbs. The sun reflects off the metal. It stings his eyes, and his skin tingles. It drains the little energy he has left. He moves around the car, chasing patches of shade. For a while, he stands on a narrow ledge at the end of a fuel tanker. It is just inches above the wheels. He cannot let himself fall asleep; one good shake of the train, and he would tumble off. What is the author’s purpose in this biography excerpt?