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The repair of double-stranded DNA breaks through non-homologous end joining (NHEJ) is a process that can lead to the deletion of part of a DNA sequence. In NHEJ, when a double-strand break occurs, the broken ends of the DNA are brought together and directly rejoined without the need for a homologous template. During this repair process, the ends of the DNA fragments may not be perfectly aligned or complementary, leading to the loss of some nucleotides at the break site. This can result in a deletion of sequences, as the repair machinery essentially "clean up" the ends of the DNA, removing any damaged nucleotides before sealing the strands together.

On the other hand, homologous recombination is a more precise repair mechanism that uses a homologous sequence as a template, generally resulting in the restoration of the original sequence and minimizing deletions. Single-stranded breaks are also repaired through different mechanisms that do not typically cause deletions in the same manner as double-stranded breaks repaired via NHEJ. Thus, the nature of the repair process in the context of a double-stranded break and the characteristics of non-homologous end joining clearly explains why this option is the most likely