Proofreading

Which one of the following statements most accurately describes proofreading?

1.Nucleotides are removed from the end of a newly made strand of DNA in the 5' to 3' direction.
2. Nucleotides are incorporated into the end of a newly made strand of DNA in the 3' to 5' direction.
3. Nucleotides are incorporated into the end of a newly made strand of DNA in the 5' to 3' direction.
4. Nucleotides are removed from the end of a newly made strand of DNA in the 3' to 5' direction.
5. Ribonucleotides are removed from Okazaki fragments and replaced with deoxyribonucleotides.