Correct option (a) plasmid
Explanation:
Plasmids are small. self replicating extra chromosomal, non-essential genetic/DNA elements. Plasmid consists of a ring of circular, supercoiled double stranded naked DNA carrying genes for replication and for one or more cellular non-essential functions.
They are ideal vectors for genetic engineering, gene cloning since, they are self-replicating, carry non-essential genes and has a restriction site for one or more restriction endonucleases.
