Answer: C. lava flow
An ecological succession is a change in the biotic community of the ecosystem with respect to change in the non-living factors and time, until the ecosystem attains stability. A primary succession occurs in a region which is completely barren and it is not able to sustain any form of life.
A primary succession begins after a lava flow because lava being a major disaster will completely destroy the soil by overlying hot magma which later on gets solidified in the form of rocks. The rate of soil production again from rocks will determine the speed of ecological succession.
