Question

Which of the following is a flightless bird?
A. Aptenodytes
B. Passer
C. Corvus
D. Pavo cristatus

Answer 1

Hint: There are so many birds on this planet, where most of them have some common features, but there are some birds that lost their characteristic features due to its adaptive changes in the process of evolution.

Complete answer:
Some of the flightless birds are ostrich and kiwi belong to the order struthioniformes, and they are commonly called as Ratites, and the other bird given here is Penguin, which belongs to the order Sphenisciformer.
Common features among all these birds are Flightless birds.
Generally, all birds have the same structure of muscles and bones are present, but it is different in flightless birds.
For example, flying birds have a structure called a keel, a ridge on the sternum, but in flightless birds, these structures are not observed.
So In Ratites flight muscles are absent, as there is no use of those muscles.
But in Penguins, the keel is somewhat retained, but here it is not used for flight, instead, it is useful for flightless aquatic existence.
When coming to forelimbs, in penguins they usually evolved into wing-like, and they have paddle-like swimming.
So from the above question, Aptenodytes-- this is two extant species of penguins as the emperor and king penguins.
Passer--genus sparrows, Corvus--Crows and ravens, Pavo cristatus-- Indian peafowl.

So the answer is Aptenodytes.

Note: Normally in flying birds, there is a light skeleton and hollow bones, as they have flown high. But in Ratites, like an ostrich, kiwi, as they have a large body, and have heavy legs and their feet are strong and thick adapted for running.