It is required to distinguish between the cells that have taken up the vector and that have not. It is done by using __________

A. multiple cloning site

B. the origin of replication

C. high copy number

D. selectable marker

Explanation: Whether the cell has taken up the vector or not is distinguished by using a selectable marker. A selectable marker often used is the ampicillin resistance property. Cells having the plasmid or vector show resistance against ampicillin.