A large deposit of sand and soil formed at the end of a river is a delta. When a river empties into the ocean, the current carrying smaller particles, such as soil and sand, slows down and eventually stops, causing these particles to be dropped off on the shore. This eventually leads to a triangular deposit, usually referred to as the mouth of the river.
Environmental and genetic factors can influence the growth of many organisms on earth such as plants, animals, and even fish. When the climate changes, many animals/organisms adapt by adaptation and evolution. Every organism can evolve in order to stay alive in this race of competition for survival. This is a natural accordance that happens every day in our world. Thus making organisms stay alive for longer periods of time.
I believe the answer is C) reproductive isolation.
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It reveals that they have relationships of being friends.