An "Indicator" in Both Research and Practice Is Best Defined

An "indicator" in both research and practice is best defined as:

A) an observation that is assumed to be evidence of the attributes or properties of something.
B) the process of describing abstract concepts by assigning numbers or other symbols to them in accordance with rules.
C) a reconceptualization of a theoretical definition on the basis of difficulties encountered in operationalizing it.
D) a variable that has been operationalized by combining a number of items into a composite score.