The answer would be letter choice B
The boundary between the crust and mantle is marked by a seismic-velocity discontinuity is called Mohorovicic discontinuity.
Mohorovicic discontinuity was discovered by Andrija Mohorovicic in 1909 who was a Croatian seismologist. He realized that the velocity of a seismic wave is related to the material's density where it is moving through. He decoded that the acceleration of the seismic waves that are observed within outer shell of the earth is a compositional change. Thus, the acceleration should be caused by a material of higher density.
It uses C. Kinetic Energy
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The answer is crystalline solid. Crystalline solids have a regular arrangement of particles, because of that, they possess definite geometry.
This means that if you take a look at the crystal under the microscope you would notice that there is a pattern that constantly repeats. This pattern is called a unit cell, and crystal is made up of stacked unit cells.