What does host range mean for a cloning vector?

Correct answer: In which hosts the vector can work

The direct answer is A: host range means the hosts in which a vector can work. A cloning vector is a DNA carrier used to introduce or maintain a foreign DNA fragment. For it to function, its origin of replication, promoter or other control elements, and selection system must be compatible with the host. Therefore, host range describes the types of cells or organisms in which the vector can replicate, be maintained, or sometimes express its inserted gene. A broad-host-range vector works in many different hosts; a narrow-host-range vector works in fewer hosts. Option A is correct because it directly defines vector host range. Option B is wrong because host colour has no role in this definition. Option C is unrelated to vector compatibility. Option D concerns the physical thickness of agar and does not tell us whether a vector functions inside a cell. The reasoning cue is simple: ask “where can this vector function?” The answer is its host range.