What is the purpose of joining DNA with a vector in genetic engineering?

Correct answer: To deliver DNA into a host cell

The direct answer is A: joining DNA with a vector is done to deliver the DNA into a host cell. A vector is a carrier molecule, commonly a plasmid, that can enter or be maintained in a suitable host and often contains an origin of replication and selectable marker. Step by step: the desired gene is prepared; it is joined to the vector using compatible ends and DNA ligase; the recombinant vector is introduced into a host cell; the host can copy the vector and sometimes express the gene. Option A is correct because delivery and maintenance of foreign DNA are the central purposes of a vector. Option B is wrong because DNA is not changed into water. Option C is wrong because destroying DNA defeats the aim of genetic engineering. Option D is wrong because DNA does not become a stone; the vector is a functional biological carrier. Memory cue: vector means vehicle—it carries the gene to the host.