How does discontinuinity relate to the earths crust

The Moho marks the transition in composition between the Earth's rocky outer crust and the more plastic mantle.  This increase of approximately 1 km/s corresponds to a distinct change in material as the waves pass through the Earth, and is commonly accepted as the lower limit of the Earth's crust.

Explanation:

This increase of approximately 1 km/s corresponds to a distinct change in material as the waves pass through the Earth, and is commonly accepted as the lower limit of the Earth's crust.

the awnser is a

it is not b or c