What Is the Difference Between Nominal and Operational Definitions

What is the difference between nominal and operational definitions?

A) A nominal definition explains a concept in words; an operational definition explains the same concept in terms of measurement.
B) A nominal definition explains a concept in terms of measurement; an operational definition explains the same concept in words.
C) A nominal definition explains a concept as the variable that will be observed for change; an operational definition explains a concept that leads to or changes another concept.
D) A nominal definition explains a concept that leads to or changes another concept; an operational definition explains a concept that will be observed for change.