Final answer:
The correct term describing a structure or substance not normally present but produced by some external force or action is 'Artifact'. This can refer to a man-made object or a foreign substance in an organism. The option (A) is correct.
Step-by-step explanation:
The term you're looking for that describes a structure or substance not normally present but produced by some external force or action is Artifact. This is an object made by a human being for a particular purpose.
In biology, the term can also refer to a substance found in an organism but not normally produced or expected to be present in that organism. In the context of archaeology or cultural studies, an artifact is any item made by humans, regardless of its skill or beauty - such as stone tools or pottery uncovered during an archaeological excavation. Therefore, option (A) is correct.