Answer:
Soil erosion causes siltation in rivers, dams, etc. In some areas, huge river deltas are formed (such as River Nile delta) because of soil erosion. Such places are good for agriculture but not good for urbanization. However, some people do not care about it, they just want to construct buildings on alluvium type soils.
Crossing over occurs at the four-strand stage when two homologous chromosomes, each consisting of a pair of sister chromatids, are paired. Each crossover involves just two of the four strands and generates two recombinant strands.
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The triangle is an Acute angle triangle.
Developing a coelom made nutrients more easily absorbed by roundworms. A coelom is a fluid filled cavity developed in the mesoderm and it is the main body of a roundworm. It contains the digestive tract and many other organs.