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: Unknown
Locard’s principle is concerned: 
Select and explain. 
A. Theory of relativity, B. Theory of decomposition, C. Theory of trauma, D. Theory of exchagnge
D: Theory of exchagnge
Answer: D: Theory of exchagnge 
Explanation: Ref. Textbook of forensic medicine. Krishnan Vij. Page. 302
 
Locard Principle:

When any two objects come into contact, there is always a transfer of material from each object on the other.
Some examples are fingerprints, footprints,hair, tool marks etc.