Which Statement Represents an Operational Definition

Which statement represents an operational definition?

A) Spirituality is a way of being or experiencing that comes about through an awareness of a transcendent dimension and one's identifiable values with regard to self, other, nature, and whatever one considers to be ultimate (Elkins, 1988) .
B) Death anxiety is an uncomfortable feeling on contemplation of one's own death (Templer, 1986) , measured by Templer's Death Anxiety Scale.
C) Maternal identity entails maternal cognitions and affect with regard to the maternal-infant relational system (Walker and Montgomery, 1994) .
D) Pain is a pattern of responses to protect the organism from harm (Sternbach, 1979) .