In recombinant DNA technology antibiotics are used:

The correct option is D As selectable markers
Recombinant DNA technology involves combining DNA molecules from two different species to generate a rDNA. This is followed by the insertion of rDNA into a host organism to produce new genetic combinations.

This technology involves various tools such as enzymes, host cells, vectors, etc.

Vectors are used in rDNA technology to carry the desired genes.

A cloning vector is a DNA molecule which can replicate autonomously. Presence of a selectable marker region is important in a vector.

The genes encoding resistance to antibiotics are usually considered as selectable markers. They help in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.

Organisms that have taken up the exogenous DNA from the surrounding environment are called transformants.

Organisms that have not taken up the exogenous DNA from the surrounding environment are called non-transformants.