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: Forensic Medicine
Exchange of trace evidence occurs, When a person comes in contact with other person . This principle is called? 
Select and explain. 
A. Locard's principle, B. Quetelet's rule, C. Petty's principle, D. None of the above
A: Locard's principle
Answer: A: Locard's principle 
Explanation: Locard's principle of Exchange 

It States that " When two objects come into contact with each other, there is always transfer of some material between them".
This is helpful in crime investigations, especially in sexual offences.