The correct option is D ELISA technique
The process of studying the symptoms in a person as a result of a disease is called diagnosis. The diagnosis can either be done through a physical examination or by reading briefly through the medical history of the patient. In some cases, tests are carried out to discover the underlying cause of a disease.
Diagnosis methods like serum and urine analysis etc. are conventional methods of disease diagnosis. They were used earlier as the only options available to detect the pathogen but with advancement in technology, techniques like recombinant DNA technology, PCR and ELISA have been developed which not only serve the purpose but help in early detection of the disease with high accuracy.
PCR (Polymerase chain reaction) is a technique used in molecular biology to create several copies of a certain DNA segment. Very low concentrations of pathogens can be detected by amplifying the DNA.
ELISA (enzyme-linked immunosorbent assay) is based on the principle of antigen-antibody interaction. The pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or antibodies synthesised against the pathogen.
Hence, the techniques that serve the purpose of early diagnosis are recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-Sorbent Assay (ELISA).