Concept:Trace elements are minerals needed by living organisms in very small amounts for normal body functions.
Explanation:Potassium, calcium, and magnesium are required in relatively large amounts, so they are classified as major or macro elements.
These major elements help in nerve transmission, bone formation, and enzyme activity.
Copper, however, is needed only in tiny quantities, mainly as a component of essential enzymes.
Because its daily requirement is extremely small, copper is an example of a trace element.
Answer:D. copper