When does dna replication happen? a. during the g1 phase of the cell cycle b. during the s phase of the cell cycle c. during the g2 phase of the cell cycle d. during the mitotic phase of the cell cycle

If you want the explanation here it is : S-Phase is the part of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase.

So answering to you question, your answer is "B. during the S phase of the cell cycle"