Locard’s principle is concerned:: (A) Theory of relativity, (B) Theory of decomposition, (C) Theory of trauma, (D) Theory of exchagnge
Answer is D. 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.