The correct answer is A, detection of the eggs in the stool.  Because even a single female worm can produce large numbers of eggs, a common method of examining stools for Ascaris eggs is the direct method, which involves mixing a small stool sample with 0.85% NaCl.  A Kato thick smear or concentration procedure may also be used.  In addition to being useful for diagnosis, egg counts can be used to measure prevalence of ascariasis.  Stool examination for eggs, however, will miss single sex infections (only male or only female worms).  These infections can still result in clinical symptoms.