Answer:
The correct answer is b. must be able to replicate autonomously & usually circular (to prevent degradation by host enzymes) and can't be too large (fragile) or too small to accept foreign DNA
Step-by-step explanation:
Vectors are plasmids which are used to transfer the desired gene fragment to its host body. Plasmids are extra-chromosomal genetic material present in bacteria and some eukaryotes that have the ability to self replicate.
Plasmids have the ability to transfer genes to other cells and this property of plasmids are used by scientist in cloning experiments so these plasmids are called vectors or plasmid vectors.
The circular form of plasmids does not allow the enzyme to get a site for degradation so its circular form prevents its degradation in the host body. Therefore the right answer is b.