What is a plasmid?
a. An organelle found in many bacteria and certain eukaryotes
b. A circular DNA molecule that replicates independently of the main chromosome(s)
c. A type of virus that has a DNA genome and infects certain types of human cells, including lung and respiratory tract tissue
d. A type of virus that has an RNA genome, codes for reverse transcriptase, and inserts a cDNA copy of its genome into cells