Microlecithal eggs are found in
A. Reptilia and Aves
B. Amphibia, Aves and Reptilia
C. Reptilia, Aves and Chiroptera
D. Eutheria

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Hint: Animals have various features which place them in different categories. One of those categories is the form in which their young ones are hatched. The animals can either lay eggs or can give birth by developing them inside their body, like humans.

Complete answer:
What are microlecithal eggs? The simple eggs having little yolk are called microlecithal. This is the basis of differentiation in the animal kingdom based on the eggs. The eggs with more yolk are called macrolecithal eggs.
Let us see which class has the microlecithal eggs.
Option A: Reptilia and Aves: Both reptilian and aves (birds) have macrolecithal eggs as they have the most yolk or there is an uneven distribution of yolk in the cytoplasm.
Option B: Amphibia, Aves and Reptilia: Amphibians have mesolecithal eggs that means that the yolk amount is more than the microlecithal ones. But the reptiles and aves have macrolecithal eggs.
Option C: Reptilia, Aves and Chiroptera: Reptiles and aves have the macrolecithal eggs that are their yolk amount are the maximum. The Chiroptera are the bats (egg-laying mammals), they also have macrolecithal eggs.
Option D: Eutheria: They are the non-egg laying mammals like humans which give birth to their young ones, they have very little/negligible yolk, so they have microlecithal eggs.

So the answer is option D: Eutheria.

Note: Eutheria is the mammal which gives birth to young ones. They are the chorioallantoic placental animals. The organ helps to provide nutrition to the fetus inside the mother's womb. Platypus, koalas are egg giving mammals.
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