Which of the following features are correct? Choose correct option. a. The origin of replication (ori) is a sequence from where replication starts and any piece of DNA linked to this sequence can be made to replicate within the host cell. b. Selectable markers help in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. c. Cloning sites are the recognition sites for restriction enzymes to ligate foreign DNA. d. pBR322 has two selectable markers: ampicillin resistance gene (ampR) and tetracycline resistance gene (tetR).