What is meant by phrase: "farmers and herders have been selectively breeding their plants and animals to produce more useful hybrids"

the answer is c) an oak tree

what have scientists found to be the most efficient and effective way to insert new sequences into an individual? a-scientists have created genetically altered foods that release dna during digestion. b-scientists use viruses to insert specific gene sequences. c-scientists irradiate genes so that they can be absorbed through the skin.