Whenever two objects are in contact, some transfer of material may occur. This is known as:

The correct answer is B. Locard’s Exchange Principle.

This principle states that whenever two objects come into contact with each other, there is always a transfer of material between them. For example, in forensic science, it implies that a criminal will leave traces (like hair or fingerprints) at a crime scene and take some material away with them, thereby providing evidence of their presence.