The correct option is D Helps to identify the cells that are transformed
After the transformation procedure, the cells are made to grow on medium that contains the antibiotic Tetracyclin. Cells that have been transformed will have the tetracyclin resistant gene incorporated and will grow in the medium in spite of the presence of tetracycline. While the non transformed cells will perish. This is called selection of transformed cell. Antiobiotic resistant genes such as genes for Tetracyclin and Amphicillin resistance are most commonly used selection markers.