Why does the author switch from narrative writing to a letter in the excerpt?

Which three parts of these excerpts reflect the idea that war affects not only the minds of the combatants but also their physical reactions?

Question 1 translate: i have to eat. question 2 translate: one must study. question 3 to make a good grade, one must pay attention. para sacar una buena nota, prestar atención. question 4 to make money, one must work. para ganar dinero, trabajar. question 5 translate: maria has to talk.

Which one event in the story almost caused them to turn back and give up? losing their donkeysthe descent into the volcanorunning into their first dead endlack of water