What causes the most destruction from earthquakes? a. when the ground shakes violently
b. when fault movement causes magma to break through the crust causing volcanoes
c. when large cracks open in the Earth's crust swallowing structures and people
d. collapsing structures, fires, electrical lines, and tsunamis

c. when large cracks open in the Earth's crust swallowing structures and people

Explanation:

Earthquakes is one of the natural events common is most areas of the earth leading to destruction of lives and properties. It varies from magnitude to level of impact which could range from mild, medium and heavy impact.

The actual destruction of the properties is not the vibration that occurs during earthquakes but rather the opening of the earth crust leading to failure of structures found within that area. For example, building crashes etc.

c, this answer is productivity.

81 is a composite number.