The correct answer is option 4: 1, 2 and 3.

1. Mass wasting: This refers to the movement of rocks and debris downhill under the influence of gravity. In this case, the massive boulder moving downhill is an example of mass wasting.

2. Erosion: This is the process of wearing away and transporting soil, rocks, or sediment by natural agents like water, wind, or ice. In this case, the heavy rains have loosened the boulder and facilitated its movement downhill, which is a result of erosion.

3. Weathering: This is the process of breaking down rocks and minerals on the Earth`s surface. Weathering can be mechanical (physical) or chemical. In this case, the heavy rains have likely contributed to the weathering of the rock, making it more susceptible to movement.

Thus, all three processes (mass wasting, erosion, and weathering) have played a role in the boulder`s movement downhill.