In the context of dna replication, what is not the purpose of the phosphate groups in the previously described molecule?

In the context of dna replication, what is not the purpose of the phosphate groups in the previously described molecule?

1. marks the molecule more stable

2. provides the energy needed for covalent bond formation

3. joins the monomer into a polymer

4. reacts with the oh group at the 3′ end of the growing strand

5. sets the stage for dehydration synthesis

What is the right answer? and Why?

Why number 5 (sets the stage..) is not the answer?