A seismologist who studies earthquakes sees that a seismic wave that traveled 500 km through Earth changed speeds multiple times. What conclusion can be drawn from this observation? (1 point)
O The seismic wave's wavelength remained constant.
O The seismic wave's frequency also changed multiple times.
O As the wave passed through less dense material, the wavelength decreased.
o As the wave passed through less dense material, the speed of the wave increased.

 Either it's B. The seismic waves frequency also changed multiple times.

or

D. As the wave passed through less dense material, the speed of the wave increased.

Explanation: I'll let you choose because I'm stumped on which one it is. They both sound like they would fit perfectly with the question and I've tried doing research on it but nothing can prove either one right or wrong for me.

I know seismic waves can change frequency given the density of rock\ground it's going through.

"The propagation velocity of seismic waves depends on density and elasticity of the medium as well as the type of wave. Velocity tends to increase with depth through Earth's crust and mantle, but drops sharply going from the mantle to outer core."

However, B. also fits nicely.

"Temperature tends to lower the speed of seismic waves and pressure tends to increase the speed. Pressure increases with depth in Earth because the weight of the rocks above gets larger with increasing depth."

Nevertheless, I hope it helps.