Answer: Option (A) is the correct answer.
Step-by-step explanation:
The movement of mass of rock is known as landslide. This movement occurs to the movement of gravity because gravity moves weakened rocks and soil that are forming sloping area of a land.
For example, earthquake makes the rocks or soil move from its initial place and as a result, landslide occurs.
Thus, we can conclude that force of gravity is the main cause of a landslide.