Locard's Exchange Principle explains that:

• A. No trace is left behind in routine contact
• B. It only applies to violent crime
• C. Transfer happens only with biological fluids
• D. Every contact leaves a trace

Answer: (D)

Locard's Exchange Principle holds that whenever two objects come into contact, there is an exchange of material between them. Because of this, every contact leaves a trace, which is why investigators search for tiny, often invisible evidence—fibers, skin cells, dust, residues, and more. This idea explains how a suspect can transfer material to a scene or a scene can leave traces on a person or item, and it underpins how forensic science connects people, places, and objects through trace evidence. The scope isn’t limited to violent crimes; any interaction involving contact can leave something behind and take something away. It’s also not restricted to biological fluids—many kinds of material can be transferred. Keep in mind that the amount of transfer can vary with how long and how hard the contact was, the surfaces involved, and environmental conditions, but the essential point remains: contact typically leaves a trace.