The hydra has a nervous system characterized by a nerve net. A nerve net is a collection of separate, but "connected" neurons. Neurons are connected by synapse. Communication between neurons can be in both directions at the synapse within a nerve net. The nerve net is concentrated around the mouth. Unlike higher animals, the hydra does not have any grouping of nerve cell bodies. In other words, there are no ganglia.
The hydra does have specialized cells for touch and chemical detection though.
The Rift Valley was formed by violent subterranean forces that tore apart the earth's crust.
You are screwed. Good luck!
The main mechanism through which the layering happened is gravity: it pulled the heavier, denser material to the center, leaving the less dense material on the surface.
The material that was on the outside cooled quicker, but this was the result, not the cause.
The answer is
<span>2) Gravity caused more-dense material to move toward the center of each planet.</span>
