Hint:Birds belong to the group of warm-blooded vertebrates. They belong to the class Aves. The characteristic features of birds include feathers, the laying of hard-shelled eggs, beaked toothless jaws, four chambered heart, high endothermic metabolic rate and strong, light-weighted and rigid bones.
Ostriches are large animals that have long legs and long necks that are protruded from the round body. They are the flightless birds that are native to the areas of Africa. Males have bold black and white coloured bodies that help them to attract females whereas females are light brown in colour.
Ostriches are considered as the biggest birds in the world. They can grow upto 2.7 meters tall and can weigh upto 320 lbs. The flat breast bones of ostrich don't have the keel that anchors the strong pectacular muscles that are used to fight. Their punny wings do not have the ability to lift the body weight above the ground.
>Penguins: they are a group of aquatic birds that are found in the southern hemisphere. Like other birds, penguins also have wings but traditionally, their wing structure evolved for swimming rather than flying. Penguins can swim at the speed of 15 to 25 miles per hour underwater.
>Hoopoes: they are the small colourful birds that are found in Asia, Africa and Europe. They are known to have a distinctive “crown” of feathers. They enjoy taking sunbathes and dust baths by spreading out their wings and tail lower to ground.
>Gallus: it is a genus of birds that include only four living species of the junglefowl. They are found in Srilanka, India and southeast Asia. They are commonly called chicken and are widespread domestic animals. Their wings are too small and the flight muscles are heavy and large because of which they can fly only a short distance.
Therefore the correct answer is option (A) Ostrich.
Note:All the birds of class Aves have three or four toes on each foot. But according to American Ostrich Association, ostriches are the only birds that have only two toes on each foot. Emu, dodo, flightless cormorant, weka, kiwi, takahe etc are some of the examples of flightless birds. Sometimes penguin species are also considered as flightless birds.