After Doing a Large-Scale Cross-Sectional Study, a Researcher Finds That

After doing a large-scale cross-sectional study, a researcher finds that each successively older group does slightly less well on a test of memory for 10-digit telephone numbers. Which of the following is the best interpretation of this result?

A) A basic biological change underlies the observed steady reduction of memory skill.
B) The differences can be explained by gender of the participants.
C) The difference has nothing to do with practice of memory skills.
D) No interpretation can be made using this result.