The correct option is : cells containing empty plasmid vectors
The blue-white screen is a technique which involves the rapid identification of the recombinant bacteria in a vector-based molecular cloning experiment. In this method, a DNA ligated vector is inserted in a host cell which is viable for transformation and grown in presence of X-gal.
The cells that are transformed with the vectors having the recombinant DNA produce the white colonies. Whereas, the cells transformed with empty vector i.e. the non-recombinant plasmids, produce the blue colonies.
b. to discover aspects of the natural world.
hopefully i .