The correct option is B Temperature
Rocks expand in the daytime due to exposure to harsh sunlight and high temperature. Rocks contract when the temperature falls rapidly. However, the outer, exposed layer extends and contracts more than the inside of the rock. It results in stress on the rock, and over time, with continuous stress and pressure, the outer surface of the stone begins to develop cracks and tend to ‘peel away’ layer by layer, like the layers of an onion.