The answer is the amputation of the lieutenant's arm. None of the other options are events in the story. The lieutenant returns home and we don't know the outcome of the battle. There is also no evidence he was ever ill.
1. Choose a story and re-read it
2. React personally. What aspects of the story do you seem to be most affected by? You should look at more than one aspect.
3. Determine the theme of the story. What is the main point? HINT: Try to complete this sentence: This story argues that …
4. Connect #2 & 3: How do you see this aspect and the theme relating
The infinitive can appear by itself, or it can be part of a larger infinitive phrase.
Examples of infinitives:
To run
To walk
To cook
To understand
To make