The correct option is A DNA ligase
DNA ligase is used to seal the nicks that remain in recombinant DNA molecule. In fact, DNA ligase joins together the neighboring nucleotides flanking a discontinuity in a DNA strand by forming a phosphodiester bond.
Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain.
The DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from one original DNA molecule.
Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end of a polynucleotide chain.