At which of the following phases does a cell replicate its DNA?

Cells replicate their DNA during the S phase of the cell cycle, which stands for "synthesis phase." This phase is specifically designated for the duplication of the cell's genetic material, ensuring that each daughter cell will receive an exact copy of the DNA when the cell eventually divides.

When considering interphase, it is important to understand that this is the phase of the cell cycle encompassing G1, S, and G2 phases. During interphase, the cell prepares for division and grows. Since the S phase is a part of interphase where DNA replication occurs, it can be accurately stated that DNA replication happens during interphase as well.

Thus, the response indicating that both S phase and interphase are involved in the process of DNA replication is correct because the S phase is the specific portion of interphase where this vital process takes place.