"a" is the most probable answer but needs some elaboration.
Spiders eat their food through a process called external digestion. The gut, intestine and esophagus of a spider are designed to take in mostly liquids. The spider regurgitates digestive fluids onto the prey to digest it working more or less as a tenderizer. Once the prey begins to liquefy, it is chewed with the jaws (chelicerae) and the fluid is sucked back into the mouth together with some liquefied "'meat" from the prey.
The spider repeats this process as often as necessary to digest and ingest all but the inedible hard parts.
When the coal reaches its hardest and the darkest form then it is termed as anthracite.
Answer: Option D
<u>Explanation:</u>
The hardest among the coal is called as the anthracite. It has large amount of carbon atoms and it is also regarded as the best quality of coal that is being mined.
This is mostly prevalent in South Korea, North Korea, United states, United Nations, Canada etc. This is mainly used in the steel making process and is combined with many alloys for enhancing their property.
Biological communities evolve through ecological succession. Ecological succession is the change in the structure and composition of species in a specific ecological community over time that can be observed. Ecological succession can occur as a natural process of time, or it can be instigated by a sudden event, a wild fire, for example. There are natural changes that occur that effect the species type and variation that exists and thrive in the communities.
Answer:
Post reproductive isolation → Hybrid sterility
Explanation:
The biological concept of species states that individuals of a species can not mate and reproduce with individuals of another species. But if they get to reproduce, the progeny will not be viable or fertile. There will not be any reproductive success.
There are different reproductive isolation mechanisms, which are barriers that inhibit or interrupt the genetic flow between different species.
Reproductive barriers are isolation mechanisms that prevent mating between two or more species. The prezygotic mechanism avoids fertilization between individuals of different species, while the postzygotic mechanism impedes the zygote to develop and reach the adult stage.
Postzygotic mechanisms or barriers include
- Hybrid inviability,
- Hybrid sterility,
- Hybrid decreased viability or fertility,
- Cytoplasmic interactions.
In the exposed example, it seems that the mountains separating the frogs´ populations made a place for the development of postzygotic barriers, specifically hybrid sterility. Frogs from one population get to mate and produce offspring with the frogs of the other population, but their progeny is sterile.