The right answer is B. Erosion.
Several phenomena lead to the creation of caves. While granite or sandstone tafoni are formed by erosion of the rock, the lava tunnels are the result of an intense magmatic activity.
Tafoni designate a rounded cavity whose dimensions vary from decimetre to several meters of depth and diameter. These cavities are formed by the erosion of grainy magmatic rocks such as granite and sandstone sedimentary rocks.
