The correct option is A Origin of replication
All of the given features are important to facilitate cloning into a vector but out of them, origin of replication (ori) is the most important one. This is due to the following reasons:
(i) Ori is a DNA sequence that is responsible for initiating replication. Any piece of DNA when linked to this sequence can replicate within the host cells.
(ii) Ori also controls the copy numbers of the linked DNA.
A selectable marker is a gene introduced into a cell, especially a bacterium or to cells in culture, that confers a trait suitable for artificial selection.
A restriction enzyme, restriction endonuclease, or restrictase is an enzyme that cleaves DNA into fragments at or near specific recognition sites within molecules known as restriction sites.