One of the most significant discoveries which allowed the development of recombinant DNA technology was:

A.	the discovery of antibiotics used for selecting transformed bacteria.
B.	the identification and isolation of restriction endonucleases permitting specific DNA cutting.
C.	the discovery of DNA and RNA polymerase allowing workers to synthesize any DNA sequence.
D.	the development of the polymerase chain reaction.
E.	the Southern technique for separation and identification of DNA sequences.