What Is the Purpose of a Selectable Marker Such as the Antibiotic-Resistance

What is the purpose of a selectable marker such as the antibiotic-resistance gene ampR?

A) Selectable markers allow a researcher to identify cells that have incorporated the recombinant plasmid.
B) Selectable markers produce antibiotics, which kill cells that have not incorporated recombinant plasmid.
C) Selectable markers prevent cells that have incorporated one plasmid from incorporating another.
D) Selectable markers allow a researcher to identify the recombinant plasmid.
E) Selectable markers are only effective in viral vectors.