This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Radio isotopes are used in the following techniques except: 
Select and explain. 
A. Mass spectroscopy, B. RIA, C. ELISA, D. Sequencing of nucleic acid
C: ELISA
Answer: C: ELISA 
Explanation: C i.e. ELISA Concept: ELISA (Enzyme Linked Inununoabsorbent Assay) is an enzyme based immnoassy; the similar test which uses radioactive isotope in place of enzyme is known as Radioimmunoassay (RIA) So I don't think any need of learning that- Nucleic acid sequencing, mass spectroscopy & RIA are tests using radio isotopes.