Answer:
The correct answer would be a. Fragments of DNA that have desired genes are isolated to form recombinant DNA for use in a host.
Genetic engineering refers to the direct manipulation or modification of the desired gene in a cell in order to produce novel or improved organism.
It includes isolation of DNA fragment that has desired gene such antibiotic resistance gene, pest resistance gene et cetera. It is done with the help of restriction endonuclease.
The isolated gene is then copied or cloned with the help of polymerase chain reaction or cloning vector.
The cloned gene is then transferred to the cell of the host organism. It can be done with the help of various techniques such as micro-injections, plasmid vectors, non-pathogenic viral vector, gene gum, T-plasmid et cetera. It depends on the type of host cell.
The transformed cell will have the desired characteristics or trait.