The correct answer is a) DNA synthesis.
The S phase, or synthesis phase, is a critical part of the cell cycle where DNA replication occurs. During this phase, each chromosome is replicated to produce two sister chromatids, ensuring that when the cell divides, each daughter cell receives an identical set of DNA. This is essential for maintaining genetic continuity and is a key preparatory step for cell division.
In contrast, protein production occurs during the G1 and G2 phases of the cell cycle. Dormancy and differentiation are processes that can happen at various stages but are not specific to the S phase. Therefore, the primary event associated with the S phase is indeed the synthesis of DNA.