The correct option is A Reverse transcriptase
Restriction endonucleases recognize specific 4-6 bp long sequences, called as restriction sites, in the DNA and cut the DNA into fragments; it does not synthesize DNA which makes option A wrong. DNA polymerase enzyme adds deoxyribonucleotides to synthesize DNA using the base sequence of parental DNA strand during DNA replication; option C wrong. The DNA synthesized using RNA template is known as cDNA or complementary DNA. RNA retroviruses have reverse transcriptase enzyme that synthesizes a DNA copy (cDNA) of viral RNA; option B is correct. Adenosine deaminase is the enzyme involved in purine metabolism; not involved in DNA synthesis which makes option D wrong.