Answer: D. mechanical weathering.
Explanation: When an exposed rock is subjected to processes like freeze-thaw it tends to break into small pieces. This process helps in shaping the landscape and is most prominent in mountain environments. The breaking of rock into small bits by forces such as the air and water is known as weathering. Whereas, mechanical weathering includes action such as thawing and freezing, along with the sudden fluctuations in temperature, the growth of plant roots between cracks in the rock and the impact of running water.
