6. Which of the following statements regarding plasmid cloning vectors is correct? (A) Circular plasmids do not require an origin of replication to be propagated in (E) coli. (B) The copy number of plasmids may vary from a few to several hundred. (C) Foreign DNA fragments up to 45,000 base pairs can be cloned in a typical plasmid. (D) Plasmids do not need to contain genes that confer resistance to antibiotics. (E) Plasmid vectors must carry promoters for inserted gene fragments.