Question

what does secondary sucession have that primary succession does not?
pioneer species
volcanos
rock
soil

Explanation:

Primary succession starts on barren, lifeless substrates like rock or volcanic rock, with no existing soil. Secondary succession occurs in areas where a previous ecosystem existed but was disturbed (e.g., fire, flood), so soil is already present to support plant growth. Pioneer species exist in both, while volcanoes/rock are associated with primary succession.

Answer:

■ Soil