Brian stresses a mineral. it breaks cleanly and evenly, leaving a smooth surface. the cleavage can be described as

If a mineral breaks and leaves a smooth crystal surface, this is said to have cleavage. There are different qualities of cleavage, depending on how smooth the surface of the plane is. For this example, since the mineral breaks cleanly and evenly, it can be described as perfect cleavage.

Answerland;

The answer is d., a mountain.