The correct option is B Gene library
A genomic library is a collection of the total genomic DNA from a single organism. Construction of a genomic library involves creating many recombinant DNA molecules. An organism's genomic DNA is extracted and then digested with a restriction enzyme. For organisms with very small genomes (~10 kb), the digested fragments can be separated by gel electrophoresis. The separated fragments can then be excised and cloned into the vector separately. However, when a large genome is digested with a restriction enzyme, there are too many fragments to excise individually. The entire set of fragments must be cloned together with the vector, and separation of clones can occur after.