This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Most commonly used vector for DNA cloning ? 
Select and explain. 
A. Plasmid, B. Virus, C. Cosmid, D. Phage
A: Plasmid
Answer: A: Plasmid 
Explanation: A cloning vector is a carrier DNA molecule to which human DNA fragment is attached. Normally, foreign DNA fragments cannot self-replicate within host cell. Therefore, they are joined to a vector DNA, that can replicate within host cell.The five major types of cloning vectors used are -i) Plasmidsii) Viral vectors/Bacteriophagesiii) Cosmidsiv) Bacterial Aificial Chromosomes (BACs)v) Yeast aificial chromosomes (YACs)