Correct Option: A

Besides nuclear DNA, bacteria possesses extranuclear DNA (outside the nucleoid region) called as plasmid which can replicate independently. Due to this property plasmid holds great importance in genetic engineering. Plasmid can be taken out of bacteria and made to combine with desired DNA segment. A plasmid carrying DNA of other organism known as cosmid, can be introduced into any desired cell. This is the basis of genetic engineering.