I think that about half of all babies are able to walk independently by 12 month of age. It said that babies tend to take their first steps from the age of 9. Babies usually start to crawl before they can walk. This is because their arm are usually more effective. After crawling they learn to stand up with their feet first and later learn to walk while holding things. The next step after that is walking.
Not all babies walk at the same time. There those that learn before the other so there is no need to worry if your child does not walk by 12 months.
Following are some examples of homologous structures.
A dolphin's flipper, bird's wing, cat's leg, and the human arm are considered homologous structures. Whereas human beings have bones such as the humerus, ulna, radius, wrist bones, and fingers, these features appear as similar bones in form in the other animals. Bats, whales, and many other animals have very similar homologous structures, demonstrating that these creatures all had a common ancestor.
The tailbone in human beings is so-named because it is a homologous structure to the beginning of many animals' tails, such as monkeys. It is known as "vestigial" because it is the last vestige of what was once a tail.
All mollusks have a "foot" that they use to travel. This foot is homologous although it may not appear to be immediately - close inspection demonstrates that in terms of form and function, gastropods, cephalopods, and bivalves share this homologous structure in common.
Mammals share the homologous structure of the vertebrae in common. For instance, in spite of its height, the giraffe has the very same number of neck bones (seven) as a giant whale and a tiny human being.
Human beings, dogs, and cats all have similar pelvises, which are homologous structures to a vestigial pair of bones that snakes have. These bones are the last remains of a pelvis, with no legs to attach.
Our eyes are homologous to the eye bulbs which blind creatures who live in caves have on their heads.
All organisms contain homologous plasma membranes with what is called a phospholipid bi-layer.
The wrist bone of the human being is homologous with the structures of many other animals, including the dolphin and the bird. A homologous structure in the panda looks like a sixth appendage, but it is actually a modified wrist bone that helps the panda bears pick leaves off the trees more dexterously.
An auditory bone that exists inside the ear of mammals is a homologous structure to the reptile's jaw bone (including the dinosaurs) as well as the jawbone of species of fish that are still in existence today.
The carpals, metacarpals, and phalanges of the human hand have homologous structures in a variety of animals, and they're not all mammals. For instance, these features are seen in penguins and reptiles as well as the mammals to which human beings are more closely related.
The genetic code among all living things is homologous - extremely similar although other genetic codes exist. This suggests a common ancestor.
Wasps and bees have stingers that they can use when they feel they are in danger. However, this is a homologous structure to the ovipositor of other organisms - the feature that allows these organisms to lay eggs.
Plants use their stomata to take in Carbon dioxide and take out oxygen during photosynthesis. It's how they "breathe" if that makes it more understandable.
Answer : A : They live in extreme environmental conditions.
