Differentiation of male and female Ascaris is based on several anatomical features. The correct answer, option 'D', states that all of the following characteristics can be used to differentiate between male and female Ascaris:
a) 5 pairs of postanal papillae
b) 50 pairs of papillae
c) Pineal setae

Let's discuss each of these characteristics in detail:

1. 5 pairs of postanal papillae:
- Postanal papillae are small, finger-like projections located in the posterior region of the body of Ascaris worms.
- In males, there are 5 pairs of postanal papillae, which are involved in copulatory activities during reproduction.
- On the other hand, females lack these postanal papillae.

2. 50 pairs of papillae:
- Papillae are small, rounded projections found on the cuticle of Ascaris worms.
- Males have 50 pairs of papillae, which are involved in holding the female during copulation.
- Females, however, do not possess papillae.

3. Pineal setae:
- Setae are bristle-like structures found in the posterior end of the male Ascaris.
- Pineal setae are a specific type of setae that are only present in male Ascaris worms.
- These setae aid in copulation by attaching to the female during mating.

In summary, the correct answer, option 'D', suggests that all of these characteristics (5 pairs of postanal papillae, 50 pairs of papillae, and pineal setae) can be used to differentiate between male and female Ascaris worms. These features are important in distinguishing the sexes of Ascaris and are particularly relevant during reproductive activities.