In this passage, O’Brien incorporates to reflect an idealized version of the man he killed.
(long sentence, short sentence, comma, dash, or semicolon)

long sentence

Explanation:

This question was asked from the literary work titled “The Man I Killed”. The book opened by describing the man whom O'Brien had killed. Below is that paragraph that captures the thought perfectly:

"HIS JAW WAS IN HIS THROAT, his upper lip and teeth were gone, his one eye was shut, his other eye was a star-shaped hole, his eyebrows were thin and arched like a woman's, his nose was undamaged, there was a slight tear at the lobe of one ear, his clean black hair was swept upward into a cowlick at the rear of the skull, his forehead was lightly freckled, his fingernails were clean, the skin at his left cheek was peeled back in three ragged strips, his right cheek was smooth and hairless, there was a butterfly on his chin, his neck was open to the spinal cord and the blood there was thick and shiny and it was this wound that had killed him. He lay face-up in the center of the trail, a slim, dead, almost dainty young man. He had bony legs, a narrow waist, long shapely fingers. His chest was sunken and poorly muscled—a scholar, maybe. His wrists were the wrists of a child. He wore a black shirt, black pyjama pants, a grey ammunition belt, a gold ring on the third finger of his right hand. His rubber sandals had been blown off. One lay beside him, the other a few meters up the trail. He had been born, maybe, in 1946 in the village of My Khe near the central coastline of Quang Ngai Province, where his parents farmed, and where his family had lived for several centuries, and where, during the time of the French, his father and two uncles and many neighbors had joined in the struggle for independence. He was not a Communist. He was a citizen and a soldier. In the village of My Khe, as in all of Quang Ngai, patriotic resistance had the force of tradition, which was partly the force of legend, and from his earliest boyhood the man I killed would have listened to stories about the heroic Trung sisters and Tran Hung Dao's famous rout of the Mongols and Le Loi's final victory against the Chinese at Tot Dong. He would have been taught that to defend the land was a man's highest duty and highest privilege. He had accepted this. It was never open to question. Secretly, though, it also frightened him. He was not a fighter. His health was poor, his body small and frail. He liked books. He wanted someday to be a teacher of mathematics. At night, lying on his mat, he could not picture himself doing the brave things his father had done, or his uncles, or the heroes of the stories. He hoped in his heart that he would never be tested. He hoped the Americans would go away. Soon, he hoped. He kept hoping and hoping, always, even when he was asleep.""

Seeing the lengthy nature of the paragraph O'Brien used to describe the man whom he killed, we can safely conclude that this is not a short sentence. This is a sentence numbering 466 words; it employed the usage of commas, dash, periods. However, this is a long sentence. Hence,

In this passage, O’Brien incorporates long sentence to reflect an idealized version of the man he killed.

themselves

an intensive pronoun is a pronoun that ends in self or selves, such as himself, herself, themselves, yourself, ourselves. since band members is a third person plural, the correct intensive pronoun would be themselves. if the band was talked about as a collective noun, itself would be the appropriate intensive pronoun. intensive pronouns are used to add emphasis to the noun it's modifying which is why it directly follows it.