Why Is Test-Retest Reliability Usually Measured Over a Short Period

Why is test-retest reliability usually measured over a short period of time (such as a few weeks) rather than over a long period of time (such as several years) ?

A) Long-term changes in people's scores might reflect real developmental changes in the trait,not just short-term fluctuation.
B) Psychological tests have not yet been developed to show high reliability over such a long interval.
C) It is very difficult to obtain measurements from the same large group of people at two points of time several years apart.
D) If a characteristic shows high test-retest reliability over a period of a few weeks,then the same result will be virtually always be observed across a period of several years.
E) None of the above;test-retest reliability usually is in fact measured over very long time periods.