Final answer:
Primary succession is the type of ecological succession that occurs in an area where no ecosystem existed before, such as bare rock with no soil.
Step-by-step explanation:
The correct answer is a. primary succession. Primary succession is the type of ecological succession that occurs in an area where no ecosystem existed before, such as bare rock with no soil. This process begins with pioneer species, such as lichens and mosses, that can tolerate harsh conditions and gradually break down the rock to form soil. Over time, more complex plant and animal species colonize the area and create a stable ecosystem.