Plasmids are considered to be a suitable vector for gene cloning because
They are small circular DNA molecules that can integrate with chromosomal host DNA.
They are small circular DNA molecules having their own replication site.
They can shuttle between eukaryotic and prokaryotic cells.
They often carry antibiotic resistance genes.
As we have already discussed in Tools of Biotechnology: Cloning Vectors & Their Types -
Plasmids are the extra-chromosomal, self-replicating, and double-stranded closed and circular DNA molecules present in the bacterial cell. Hence, the correct option is (b).