The answer is B- Embryological Development.
Pyroclastic materials are classified according to their size, measured in milli meters: dust (less than 0.6 mm [0.02 inch]), ash (fragments between 0.6 and 2 mm [0.02 to 0.08 inch]), cinders (fragments between 2 and 64 mm [0.08 and 2.5 inches], also known as lapilli), blocks (angular fragments greater than 64 mm), and bombs (rounded fragments greater than 64 mm).
The fluid nature of a pyroclastic flow is maintained by the turbulence of its internal gases. Both the incandescent pyroclastic particles and the rolling clouds of dust that rise above them actively liberate more gas. The expansion of these gases accounts for the nearly frictionless character of the flow as well as its great mobility and destructive power.
Pyroclastic flow, in a volcanic eruption, a fluidized mixture of hot rock fragments, hot gases, and entrapped air that moves at high speed in thick, gray-to-black, turbulent clouds that hug the ground. The temperature of the volcanic gases can reach about 600 to 700 °C (1,100 to 1,300 °F). The velocity of a flow often exceeds 100 km (60 miles) per hour and may attain speeds as great as 160 km (100 miles) per hour.
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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.
