Primary succession is a process that occurs in lifeless areas where soil has not yet formed. In the context of the provided options, the event that could cause primary succession to begin is d) volcanic eruption.
A volcanic eruption creates new land by depositing lava, which eventually cools and solidifies into rock. Initially, this area lacks soil and living organisms, providing a blank slate for ecological development. Over time, as weathering breaks down the rock into smaller particles, soil formation begins, allowing pioneering species like lichens and mosses to establish themselves.
In contrast, a forest fire (a) can lead to secondary succession, where the soil already exists. A severe storm (b) might also result in some changes to the environment but typically does not create the conditions for primary succession since soil is already present. The abandonment of farmland (c) would likewise lead to secondary succession, as the soil remains intact and seeds may already be present.