The opportunity cost of choosing a particular activity:

A) can be easily and accurately calculated.
B) cannot be estimated.
C) does not change over time.
D) varies depending on time and circumstances.
E) is measured by the money spent on the activity.

Varies

Describes how something changes or differs across different situations, locations, or points in time.

Time

A continuum that lacks spatial dimensions and in which events occur in apparently irreversible succession from the past, through the present, into the future.

Circumstances

The conditions or facts affecting a particular event or situation, often influencing the outcome or actions of individuals.