Final answer:
Upon arrival at Buna, Eliezer is most fixated on staying close to his father's side as they are being assigned to the Kommandos. His determination to stay with his father reflects the centrality of their relationship in the memoir 'Night'.
Step-by-step explanation:
The student's question pertains to the character Eliezer from the memoir Night by Elie Wiesel. When Eliezer arrives at Buna, and they are being assigned to the Kommandos, the statement that best describes what he is most fixated on is c) Staying close to his father's side. Throughout their ordeal in the concentration camps, Eliezer's primary concern is his father's well-being, and he is desperate to remain with him at all costs. This bond is a central theme of the memoir and is highlighted by their arrival at Buna, where he fears, separation might lead to losing his father, the only family member he has left with him.