Ans. Option (B).
In genetic engineering, a vector molecule can be defined as a molecule of DNA, which is used as a vehicle to artificially transport foreign gene or DNA material into another organism (host) or cell, where it can be copied or/and expressed.
To make a recombinant cell or organism, the target DNA is first isolated and then integrated with the vector molecule. The recombinant DNA (having target DNA) is then inserted to host organism where it makes its copies.
A well known example of vector molecule is plasmid DNA, found in many bacterial and some eukaryotic cells.
Thus, the correct answer is option (B).