Black beach sand originates from broken down what?

Sand grains are formed when rock or other hard material is broken down by waves, a process that can take thousands of years. Beaches with pebbles or course sand are very young while beaches with fine sand are older. The color of sand grains comes from the original material that formed the sand.

Black sand is made of broken down fragments of volcanic rock. When a volcano erupts, lava pours out, cools down, and creates black rocks. The waves erode and break down this rock causing for black sand to be created.

the answer to your question is c.

if you read the house of usher you should know that the house was haunted

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.